Revert "Disable setting a library tag handler."

runtime/dart_isolate.cc

@@ -184,6 +184,11 @@ bool DartIsolate::Initialize(Dart_Isolate dart_isolate) {
 
   SetMessageHandlingTaskRunner(GetTaskRunners().GetUITaskRunner());
 
+  if (tonic::LogIfError(
+          Dart_SetLibraryTagHandler(tonic::DartState::HandleLibraryTag))) {
+    return false;
+  }
+
   if (!UpdateThreadPoolNames()) {
     return false;
   }
@@ -618,9 +623,10 @@ Dart_Isolate DartIsolate::DartCreateAndStartServiceIsolate(
 
   tonic::DartState::Scope scope(service_isolate);
   if (!DartServiceIsolate::Startup(
-          settings.observatory_host,  // server IP address
-          settings.observatory_port,  // server observatory port
-          false,                      //  disable websocket origin check
+          settings.observatory_host,           // server IP address
+          settings.observatory_port,           // server observatory port
+          tonic::DartState::HandleLibraryTag,  // embedder library tag handler
+          false,  //  disable websocket origin check
           settings.disable_service_auth_codes,  // disable VM service auth codes
           error                                 // error (out)
           )) {

runtime/dart_service_isolate.cc

@@ -30,6 +30,7 @@
 namespace flutter {
 namespace {
 
+static Dart_LibraryTagHandler g_embedder_tag_handler;
 static tonic::DartLibraryNatives* g_natives;
 static std::string g_observatory_uri;
 
@@ -126,12 +127,17 @@ void DartServiceIsolate::Shutdown(Dart_NativeArguments args) {
 
 bool DartServiceIsolate::Startup(std::string server_ip,
                                  intptr_t server_port,
+                                 Dart_LibraryTagHandler embedder_tag_handler,
                                  bool disable_origin_check,
                                  bool disable_service_auth_codes,
                                  char** error) {
   Dart_Isolate isolate = Dart_CurrentIsolate();
   FML_CHECK(isolate);
 
+  // Remember the embedder's library tag handler.
+  g_embedder_tag_handler = embedder_tag_handler;
+  FML_CHECK(g_embedder_tag_handler);
+
   // Setup native entries.
   if (!g_natives) {
     g_natives = new tonic::DartLibraryNatives();

runtime/dart_service_isolate.h

@@ -23,6 +23,7 @@ class DartServiceIsolate {
 
   static bool Startup(std::string server_ip,
                       intptr_t server_port,
+                      Dart_LibraryTagHandler embedder_tag_handler,
                       bool disable_origin_check,
                       bool disable_service_auth_codes,
                       char** error);