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&);
+    ~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, 2017/02/03 23:42:32]

Hmm this feels like a wrong place to put this. How different would this patch
look if we pass image_to_skip as a separate argument to the functions that need
it?

In other words, I want to avoid having PlaybackSettings as a general grab bag of
parameters we want to plumb. This is the reason why for example rect/scale are
passed separately.

What do you think?

[Khushal, 2017/02/07 00:25:32]

It will be a lot of plumbing. The set has to finally reach the ImageHijackCanvas
in RasterSource::PlaybackToCanvas. And it starts from RasterTaskImpl. So
RasterTaskImpl->RasterBuffer->RasterBufferProvider->RasterSource::PlaybackToCanvas->RasterSource::PlaybackToCanvas
(which finally creates the ImageHijackCanvas. The plumbing is fine, but I don't
see much advantage from it. In general every setting that concerns with how we
deal with images during raster is here so it felt better to keep that
consolidated in one place.

   };
 
   static scoped_refptr<RasterSource> CreateFromRecordingSource(