diff --git a/lib/ui/annotations.dart b/lib/ui/annotations.dart
index 825c8637b22e8..c9a41e7c1979c 100644
--- a/lib/ui/annotations.dart
+++ b/lib/ui/annotations.dart
@@ -39,7 +39,7 @@ part of dart.ui;
 ///   }
 /// }
 /// ```
-const _KeepToString keepToString = _KeepToString();
+const _KeepToString/*!*/ keepToString = _KeepToString();
 
 class _KeepToString {
   const _KeepToString();
diff --git a/lib/ui/channel_buffers.dart b/lib/ui/channel_buffers.dart
index 4b8f805dd4723..dbffda34c003a 100644
--- a/lib/ui/channel_buffers.dart
+++ b/lib/ui/channel_buffers.dart
@@ -130,7 +130,7 @@ class ChannelBuffers {
   }
 
   /// Returns true on overflow.
-  bool push(String channel, ByteData data, PlatformMessageResponseCallback callback) {
+  bool push(String/*!*/ channel, ByteData/*!*/ data, PlatformMessageResponseCallback/*!*/ callback) {
     _RingBuffer<_StoredMessage> queue = _messages[channel];
     if (queue == null) {
       queue = _makeRingBuffer(kDefaultBufferSize);
@@ -182,7 +182,7 @@ class ChannelBuffers {
   ///
   /// This should be called once a channel is prepared to handle messages
   /// (i.e. when a message handler is setup in the framework).
-  Future<void> drain(String channel, DrainChannelCallback callback) async {
+  Future<void> drain(String/*!*/ channel, DrainChannelCallback/*!*/ callback) async {
     while (!_isEmpty(channel)) {
       final _StoredMessage message = _pop(channel);
       await callback(message.data, message.callback);
@@ -204,7 +204,7 @@ class ChannelBuffers {
   ///   Arity: 2
   ///   Format: `resize\r<channel name>\r<new size>`
   ///   Description: Allows you to set the size of a channel's buffer.
-  void handleMessage(ByteData data) {
+  void handleMessage(ByteData/*!*/ data) {
     final List<String> command = _getString(data).split('\r');
     if (command.length == /*arity=*/2 + 1 && command[0] == 'resize') {
       _resize(command[1], int.parse(command[2]));
@@ -220,4 +220,4 @@ class ChannelBuffers {
 ///
 /// See also:
 /// * [BinaryMessenger] - The place where ChannelBuffers are typically read.
-final ChannelBuffers channelBuffers = ChannelBuffers();
+final ChannelBuffers/*!*/ channelBuffers = ChannelBuffers();
diff --git a/lib/ui/hash_codes.dart b/lib/ui/hash_codes.dart
index e5b8b67527139..3242727e19b1e 100644
--- a/lib/ui/hash_codes.dart
+++ b/lib/ui/hash_codes.dart
@@ -40,14 +40,14 @@ class _Jenkins {
 /// ```dart
 /// int hashCode => hashValues(foo, bar, hashList(quux), baz);
 /// ```
-int hashValues(
-  Object arg01,            Object arg02,          [ Object arg03 = _hashEnd,
-  Object arg04 = _hashEnd, Object arg05 = _hashEnd, Object arg06 = _hashEnd,
-  Object arg07 = _hashEnd, Object arg08 = _hashEnd, Object arg09 = _hashEnd,
-  Object arg10 = _hashEnd, Object arg11 = _hashEnd, Object arg12 = _hashEnd,
-  Object arg13 = _hashEnd, Object arg14 = _hashEnd, Object arg15 = _hashEnd,
-  Object arg16 = _hashEnd, Object arg17 = _hashEnd, Object arg18 = _hashEnd,
-  Object arg19 = _hashEnd, Object arg20 = _hashEnd ]) {
+int/*!*/ hashValues(
+  Object/*?*/ arg01,            Object/*?*/ arg02,          [ Object/*?*/ arg03 = _hashEnd,
+  Object/*?*/ arg04 = _hashEnd, Object/*?*/ arg05 = _hashEnd, Object/*?*/ arg06 = _hashEnd,
+  Object/*?*/ arg07 = _hashEnd, Object/*?*/ arg08 = _hashEnd, Object/*?*/ arg09 = _hashEnd,
+  Object/*?*/ arg10 = _hashEnd, Object/*?*/ arg11 = _hashEnd, Object/*?*/ arg12 = _hashEnd,
+  Object/*?*/ arg13 = _hashEnd, Object/*?*/ arg14 = _hashEnd, Object/*?*/ arg15 = _hashEnd,
+  Object/*?*/ arg16 = _hashEnd, Object/*?*/ arg17 = _hashEnd, Object/*?*/ arg18 = _hashEnd,
+  Object/*?*/ arg19 = _hashEnd, Object/*?*/ arg20 = _hashEnd ]) {
   int result = 0;
   result = _Jenkins.combine(result, arg01);
   result = _Jenkins.combine(result, arg02);
@@ -112,7 +112,7 @@ int hashValues(
 /// Combine the [Object.hashCode] values of an arbitrary number of objects from
 /// an [Iterable] into one value. This function will return the same value if
 /// given null as if given an empty list.
-int hashList(Iterable<Object> arguments) {
+int/*!*/ hashList(Iterable<Object/*?*/>/*!*/ arguments) {
   int result = 0;
   if (arguments != null) {
     for (Object argument in arguments)
diff --git a/lib/ui/lerp.dart b/lib/ui/lerp.dart
index 00cc3bdfd366a..d61c23dff0c2d 100644
--- a/lib/ui/lerp.dart
+++ b/lib/ui/lerp.dart
@@ -6,7 +6,7 @@
 part of dart.ui;
 
 /// Linearly interpolate between two numbers.
-double lerpDouble(num a, num b, double t) {
+double/*!*/ lerpDouble(num/*?*/ a, num/*?*/ b, double/*!*/ t) {
   if (a == null && b == null)
     return null;
   a ??= 0.0;
diff --git a/lib/web_ui/lib/src/ui/annotations.dart b/lib/web_ui/lib/src/ui/annotations.dart
index 10b9ef2694b1f..4af5f3b5e3fee 100644
--- a/lib/web_ui/lib/src/ui/annotations.dart
+++ b/lib/web_ui/lib/src/ui/annotations.dart
@@ -39,7 +39,7 @@ part of ui;
 ///   }
 /// }
 /// ```
-const _KeepToString keepToString = _KeepToString();
+const _KeepToString/*!*/ keepToString = _KeepToString();
 
 class _KeepToString {
   const _KeepToString();
diff --git a/lib/web_ui/lib/src/ui/channel_buffers.dart b/lib/web_ui/lib/src/ui/channel_buffers.dart
index b762e96a0dae9..d67a90efe831e 100644
--- a/lib/web_ui/lib/src/ui/channel_buffers.dart
+++ b/lib/web_ui/lib/src/ui/channel_buffers.dart
@@ -130,7 +130,7 @@ class ChannelBuffers {
   }
 
   /// Returns true on overflow.
-  bool push(String channel, ByteData data, PlatformMessageResponseCallback callback) {
+  bool push(String/*!*/ channel, ByteData/*!*/ data, PlatformMessageResponseCallback/*!*/ callback) {
     _RingBuffer<_StoredMessage> queue = _messages[channel];
     if (queue == null) {
       queue = _makeRingBuffer(kDefaultBufferSize);
@@ -182,7 +182,7 @@ class ChannelBuffers {
   ///
   /// This should be called once a channel is prepared to handle messages
   /// (i.e. when a message handler is setup in the framework).
-  Future<void> drain(String channel, DrainChannelCallback callback) async {
+  Future<void> drain(String/*!*/ channel, DrainChannelCallback/*!*/ callback) async {
     while (!_isEmpty(channel)) {
       final _StoredMessage message = _pop(channel);
       await callback(message.data, message.callback);
@@ -204,7 +204,7 @@ class ChannelBuffers {
   ///   Arity: 2
   ///   Format: `resize\r<channel name>\r<new size>`
   ///   Description: Allows you to set the size of a channel's buffer.
-  void handleMessage(ByteData data) {
+  void handleMessage(ByteData/*!*/ data) {
     final List<String> command = _getString(data).split('\r');
     if (command.length == /*arity=*/2 + 1 && command[0] == 'resize') {
       _resize(command[1], int.parse(command[2]));
@@ -220,4 +220,4 @@ class ChannelBuffers {
 ///
 /// See also:
 /// * [BinaryMessenger] - The place where ChannelBuffers are typically read.
-final ChannelBuffers channelBuffers = ChannelBuffers();
+final ChannelBuffers/*!*/ channelBuffers = ChannelBuffers();
diff --git a/lib/web_ui/lib/src/ui/hash_codes.dart b/lib/web_ui/lib/src/ui/hash_codes.dart
index 70428a8301c3d..3eca5ce28302f 100644
--- a/lib/web_ui/lib/src/ui/hash_codes.dart
+++ b/lib/web_ui/lib/src/ui/hash_codes.dart
@@ -42,14 +42,14 @@ class _Jenkins {
 /// ```dart
 /// int hashCode => hashValues(foo, bar, hashList(quux), baz);
 /// ```
-int hashValues(
-  Object arg01,            Object arg02,          [ Object arg03 = _hashEnd,
-  Object arg04 = _hashEnd, Object arg05 = _hashEnd, Object arg06 = _hashEnd,
-  Object arg07 = _hashEnd, Object arg08 = _hashEnd, Object arg09 = _hashEnd,
-  Object arg10 = _hashEnd, Object arg11 = _hashEnd, Object arg12 = _hashEnd,
-  Object arg13 = _hashEnd, Object arg14 = _hashEnd, Object arg15 = _hashEnd,
-  Object arg16 = _hashEnd, Object arg17 = _hashEnd, Object arg18 = _hashEnd,
-  Object arg19 = _hashEnd, Object arg20 = _hashEnd ]) {
+int/*!*/ hashValues(
+  Object/*?*/ arg01,            Object/*?*/ arg02,          [ Object/*?*/ arg03 = _hashEnd,
+  Object/*?*/ arg04 = _hashEnd, Object/*?*/ arg05 = _hashEnd, Object/*?*/ arg06 = _hashEnd,
+  Object/*?*/ arg07 = _hashEnd, Object/*?*/ arg08 = _hashEnd, Object/*?*/ arg09 = _hashEnd,
+  Object/*?*/ arg10 = _hashEnd, Object/*?*/ arg11 = _hashEnd, Object/*?*/ arg12 = _hashEnd,
+  Object/*?*/ arg13 = _hashEnd, Object/*?*/ arg14 = _hashEnd, Object/*?*/ arg15 = _hashEnd,
+  Object/*?*/ arg16 = _hashEnd, Object/*?*/ arg17 = _hashEnd, Object/*?*/ arg18 = _hashEnd,
+  Object/*?*/ arg19 = _hashEnd, Object/*?*/ arg20 = _hashEnd ]) {
   int result = 0;
   result = _Jenkins.combine(result, arg01);
   result = _Jenkins.combine(result, arg02);
@@ -114,7 +114,7 @@ int hashValues(
 /// Combine the [Object.hashCode] values of an arbitrary number of objects from
 /// an [Iterable] into one value. This function will return the same value if
 /// given null as if given an empty list.
-int hashList(Iterable<Object> arguments) {
+int/*!*/ hashList(Iterable<Object/*?*/>/*!*/ arguments) {
   int result = 0;
   if (arguments != null) {
     for (Object argument in arguments)
diff --git a/lib/web_ui/lib/src/ui/lerp.dart b/lib/web_ui/lib/src/ui/lerp.dart
index 1f09fb96e39db..8d062cf385ecc 100644
--- a/lib/web_ui/lib/src/ui/lerp.dart
+++ b/lib/web_ui/lib/src/ui/lerp.dart
@@ -6,7 +6,7 @@
 part of ui;
 
 /// Linearly interpolate between two numbers.
-double lerpDouble(num a, num b, double t) {
+double/*!*/ lerpDouble(num/*?*/ a, num/*?*/ b, double/*!*/ t) {
   if (a == null && b == null) {
     return null;
   }