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

media/base/video_frame.h

Index: media/base/video_frame.h
diff --git a/media/base/video_frame.h b/media/base/video_frame.h
index 366a356735ab9ab1e8c57039321d779202005022..8470d1bb140015602934208ea1c09b1b08330d7b 100644
--- a/media/base/video_frame.h
+++ b/media/base/video_frame.h
@@ -11,6 +11,7 @@
 #include "base/md5.h"
 #include "base/memory/shared_memory.h"
 #include "base/synchronization/lock.h"
+#include "base/values.h"
 #include "media/base/buffers.h"
 #include "ui/gfx/geometry/rect.h"
 #include "ui/gfx/geometry/size.h"
@@ -68,6 +69,11 @@ class MEDIA_EXPORT VideoFrame : public base::RefCountedThreadSafe<VideoFrame> {
     FORMAT_MAX = YV12HD,  // Must always be equal to largest entry logged.
   };
 
+  // Key for getting/setting the frame rate value (of type DoubleValue) in the
+  // metadata dictionary.  The value represents either the fixed frame rate, or
+  // the maximum frame rate to expect from a variable-rate source.
+  static const char kFrameRateMetadataKey[];
+
   // Returns the name of a Format as a string.
   static std::string FormatToString(Format format);
 
@@ -288,6 +294,15 @@ class MEDIA_EXPORT VideoFrame : public base::RefCountedThreadSafe<VideoFrame> {
   // Returns the offset into the shared memory where the frame data begins.
   size_t shared_memory_offset() const;
 
+  // Returns a dictionary of optional metadata.  This contains information
+  // associated with the frame that downstream clients might use for frame-level
+  // logging, quality/performance optimizations, signaling, etc.
+  //
+  // TODO(miu): Move some of the "extra" members of VideoFrame (below) into
+  // here as a later clean-up step.
+  const base::DictionaryValue& metadata() const { return metadata_; }
+  base::DictionaryValue& metadata() { return metadata_; }
+
   bool allow_overlay() const { return allow_overlay_; }
 
 #if defined(OS_POSIX)
@@ -403,6 +418,8 @@ class MEDIA_EXPORT VideoFrame : public base::RefCountedThreadSafe<VideoFrame> {
 
   const bool end_of_stream_;
 
+  base::DictionaryValue metadata_;
+
   bool allow_overlay_;
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(VideoFrame);