Address comments

Author: bdero

ci/licenses_golden/licenses_flutter

@@ -176,6 +176,7 @@ FILE: ../../../flutter/fml/dart/dart_converter.h
 FILE: ../../../flutter/fml/delayed_task.cc
 FILE: ../../../flutter/fml/delayed_task.h
 FILE: ../../../flutter/fml/eintr_wrapper.h
+FILE: ../../../flutter/fml/endianness.cc
 FILE: ../../../flutter/fml/endianness.h
 FILE: ../../../flutter/fml/endianness_unittests.cc
 FILE: ../../../flutter/fml/file.cc

fml/BUILD.gn

@@ -21,6 +21,8 @@ source_set("fml") {
     "delayed_task.cc",
     "delayed_task.h",
     "eintr_wrapper.h",
+    "endianness.cc",
+    "endianness.h",
     "file.cc",
     "file.h",
     "hash_combine.h",

fml/endianness.cc

@@ -0,0 +1,5 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "flutter/fml/endianness.h"

fml/endianness.h

@@ -14,29 +14,29 @@
 #include "flutter/fml/build_config.h"
 
 // Compiler intrinsics for flipping endianness.
-#define BYTESWAP16(n) __builtin_bswap16(n)
-#define BYTESWAP32(n) __builtin_bswap32(n)
-#define BYTESWAP64(n) __builtin_bswap64(n)
+#define FML_BYTESWAP_16(n) __builtin_bswap16(n)
+#define FML_BYTESWAP_32(n) __builtin_bswap32(n)
+#define FML_BYTESWAP_64(n) __builtin_bswap64(n)
 
 #if defined(_MSC_VER)
-#define BYTESWAP16(n) _byteswap_ushort(n)
-#define BYTESWAP32(n) _byteswap_ulong(n)
-#define BYTESWAP64(n) _byteswap_uint64(n)
+#define FML_BYTESWAP_16(n) _byteswap_ushort(n)
+#define FML_BYTESWAP_32(n) _byteswap_ulong(n)
+#define FML_BYTESWAP_64(n) _byteswap_uint64(n)
 #endif
 
 namespace fml {
 
 /// @brief  Flips the endianness of the given value.
-template <typename T>
+template <typename T, class = std::enable_if_t<std::is_integral_v<T>>>
 constexpr T ByteSwap(T n) {
   if constexpr (sizeof(T) == 1) {
     return n;
   } else if constexpr (sizeof(T) == 2) {
-    return (T)BYTESWAP16((uint16_t)n);
+    return (T)FML_BYTESWAP_16((uint16_t)n);
   } else if constexpr (sizeof(T) == 4) {
-    return (T)BYTESWAP32((uint32_t)n);
+    return (T)FML_BYTESWAP_32((uint32_t)n);
   } else if constexpr (sizeof(T) == 8) {
-    return (T)BYTESWAP64((uint64_t)n);
+    return (T)FML_BYTESWAP_64((uint32_t)n);
   } else {
     static_assert(!sizeof(T), "Unsupported size");
   }