Add metadata to media::VideoFrame and plumb it through IPC/MediaStream.

media/media.gyp

Index: media/media.gyp
diff --git a/media/media.gyp b/media/media.gyp
index 3f95cc8e6ad97812c4f352941fc56d87fc47eb8e..ea044b9ad50506840e60a374d6c68898f9a1058f 100644
--- a/media/media.gyp
+++ b/media/media.gyp
@@ -388,6 +388,8 @@
         'base/video_decoder_config.h',
         'base/video_frame.cc',
         'base/video_frame.h',
+        'base/video_frame_metadata.cc',
+        'base/video_frame_metadata.h',
         'base/video_frame_pool.cc',
         'base/video_frame_pool.h',
         'base/video_renderer.cc',
@@ -1889,6 +1891,8 @@
             'base/mac/videotoolbox_glue.mm',
             'base/video_frame.cc',
             'base/video_frame.h',
+            'base/video_frame_metadata.cc',
+            'base/video_frame_metadata.h',
           ],
           'link_settings': {
             'libraries': [