cc: Add image decode control in the compositor.

cc/playback/discardable_image_map.h

Index: cc/playback/discardable_image_map.h
diff --git a/cc/playback/discardable_image_map.h b/cc/playback/discardable_image_map.h
index db6b17fed3405369ee3e8cb3c7544bf5760d3863..0b32e78e2d45e16bfda9ba401384538e00a7735d 100644
--- a/cc/playback/discardable_image_map.h
+++ b/cc/playback/discardable_image_map.h
@@ -20,6 +20,13 @@ class SkImage;
 
 namespace cc {
 
+// Helper function to apply the matrix to the rect and return the result.
+SkRect MapRect(const SkMatrix& matrix, const SkRect& src);
+
+// Helper funciton to extract a scale from the matrix. Returns true on success
+// and false on failure.
+bool ExtractScale(const SkMatrix& matrix, SkSize* scale);
+
 // This class is used for generating discardable images data (see DrawImage
 // for the type of data it stores). It allows the client to query a particular
 // rect and get back a list of DrawImages in that rect.