add colortable support to imagegenerator

src/lazy/SkDiscardablePixelRef.h

Index: src/lazy/SkDiscardablePixelRef.h
diff --git a/src/lazy/SkDiscardablePixelRef.h b/src/lazy/SkDiscardablePixelRef.h
index e5e1c9f0e19e50a54056664c3c91cf548afe7748..52a1d6ce3708d1df1db1bccf5bff93daa223bb43 100644
--- a/src/lazy/SkDiscardablePixelRef.h
+++ b/src/lazy/SkDiscardablePixelRef.h
@@ -17,10 +17,6 @@
  *  A PixelRef backed by SkDiscardableMemory, with the ability to
  *  re-generate the pixels (via a SkImageGenerator) if the DM is
  *  purged.
- *
- *  Since SkColorTable is reference-counted, we do not support indexed
- *  color with this class; there would be no way for the discardable
- *  memory system to unref the color table.
  */
 class SkDiscardablePixelRef : public SkPixelRef {
 public:
@@ -46,6 +42,7 @@ private:
     // PixelRef, since the SkBitmap doesn't expect them to change.
 
     SkDiscardableMemory* fDiscardableMemory;
+    SkAutoTUnref<SkColorTable> fCTable;
 
     /* Takes ownership of SkImageGenerator. */
     SkDiscardablePixelRef(const SkImageInfo&, SkImageGenerator*,