Add struct traits for base::Value.

media/base/video_frame_metadata.cc

Index: media/base/video_frame_metadata.cc
diff --git a/media/base/video_frame_metadata.cc b/media/base/video_frame_metadata.cc
index 5d670a197250c755aa58a3fae81da1133be55f6f..3bc108683c7cb605b9e740ea9ee47013a62d0e26 100644
--- a/media/base/video_frame_metadata.cc
+++ b/media/base/video_frame_metadata.cc
@@ -151,9 +151,9 @@ bool VideoFrameMetadata::IsTrue(Key key) const {
   return GetBoolean(key, &value) && value;
 }
 
-void VideoFrameMetadata::MergeInternalValuesInto(
-    base::DictionaryValue* out) const {
-  out->MergeDictionary(&dictionary_);
+std::unique_ptr<base::DictionaryValue> VideoFrameMetadata::CopyInternalValues()

[dcheng, 2016/12/20 23:44:47]

It's a bit unfortunate that we have to copy now, just to serialize for IPC.

[Sam McNally, 2016/12/21 00:16:15]

Yes, but it's no worse than before. Merging the dictionary copied the contents
into |out|.

+    const {
+  return dictionary_.CreateDeepCopy();
 }
 
 void VideoFrameMetadata::MergeInternalValuesFrom(