cc: Add checker-imaging support to TileManager.

cc/playback/raster_source.h

Index: cc/playback/raster_source.h
diff --git a/cc/playback/raster_source.h b/cc/playback/raster_source.h
index 29ca3889827d1d7d5d32dd482de10943fb0f9290..b50ff427dc425046b523f652885c426fc815c4c7 100644
--- a/cc/playback/raster_source.h
+++ b/cc/playback/raster_source.h
@@ -31,6 +31,8 @@ class CC_EXPORT RasterSource : public base::RefCountedThreadSafe<RasterSource> {
  public:
   struct CC_EXPORT PlaybackSettings {
     PlaybackSettings();
+    PlaybackSettings(const PlaybackSettings&);

[vmpstr, 2017/02/10 19:25:42]

Might as well add a move ctor too

[Khushal, 2017/02/10 22:09:19]

Done.

+    ~PlaybackSettings();
 
     // If set to true, this indicates that the canvas has already been
     // rasterized into. This means that the canvas cannot be cleared safely.
@@ -42,6 +44,10 @@ class CC_EXPORT RasterSource : public base::RefCountedThreadSafe<RasterSource> {
     // If set to true, we will use an image hijack canvas, which enables
     // compositor image caching.
     bool use_image_hijack_canvas;
+
+    // If non-empty, an image hijack canvas will be used to skip these images
+    // during raster.
+    std::unordered_set<ImageId> images_to_skip;

[vmpstr, 2017/02/10 19:25:42]

Can you file a TODO/bug to rethink how we pass things to Playback from tile
manager. I think what you have here is good, but I wanna see if we want to move
more settings there and/or rename PlaybackSettings to something more
descriptive.

[Khushal, 2017/02/10 22:09:19]

Done.

   };
 
   static scoped_refptr<RasterSource> CreateFromRecordingSource(