Implement MediaMetadata artwork in content

content/public/common/media_metadata.h

Index: content/public/common/media_metadata.h
diff --git a/content/public/common/media_metadata.h b/content/public/common/media_metadata.h
index 3d7f13c59366caac20a29ed98b79c0d8a8478d58..22e325e242eea8d04a26aa7d961d786c6c32e7da 100644
--- a/content/public/common/media_metadata.h
+++ b/content/public/common/media_metadata.h
@@ -5,14 +5,20 @@
 #ifndef CONTENT_PUBLIC_COMMON_MEDIA_METADATA_H_
 #define CONTENT_PUBLIC_COMMON_MEDIA_METADATA_H_
 
+#include <vector>
+
 #include "base/strings/string16.h"
 #include "content/common/content_export.h"
+#include "content/public/common/manifest.h"
 
 namespace content {
 
 // The MediaMetadata is a structure carrying information associated to a
 // content::MediaSession.
 struct CONTENT_EXPORT MediaMetadata {
+  // TODO(zqzhang): move |Manifest::Icon| to a common place.
+  using Artwork = Manifest::Icon;
+
   MediaMetadata();
   ~MediaMetadata();
 
@@ -28,6 +34,8 @@ struct CONTENT_EXPORT MediaMetadata {
   // Album associated to the MediaSession.
   base::string16 album;
 
+  std::vector<Artwork> artwork;
+
   // Maximum length for all the strings inside the MediaMetadata when it is sent
   // over IPC. The renderer process should truncate the strings before sending
   // the MediaMetadata and the browser process must do the same when receiving