add encodeData() to SkImageEncoder, and add encoding to SkImage

src/image/SkImage_Raster.cpp

Index: src/image/SkImage_Raster.cpp
diff --git a/src/image/SkImage_Raster.cpp b/src/image/SkImage_Raster.cpp
index 4a18f4aef22aeb0b7ee32ac94ba7f676721ebe90..5e1e8a02f3ef3ef72098fb279acc4b2794202c92 100644
--- a/src/image/SkImage_Raster.cpp
+++ b/src/image/SkImage_Raster.cpp
@@ -55,6 +55,7 @@ public:
     virtual ~SkImage_Raster();
 
     virtual void onDraw(SkCanvas*, SkScalar, SkScalar, const SkPaint*) SK_OVERRIDE;
+    virtual bool getROPixels(SkBitmap*) const SK_OVERRIDE;
 
     // exposed for SkSurface_Raster via SkNewImageFromPixelRef
     SkImage_Raster(const SkImage::Info&, SkPixelRef*, size_t rowBytes);
@@ -108,6 +109,11 @@ void SkImage_Raster::onDraw(SkCanvas* canvas, SkScalar x, SkScalar y, const SkPa
     canvas->drawBitmap(fBitmap, x, y, paint);
 }
 
+bool SkImage_Raster::getROPixels(SkBitmap* dst) const {
+    *dst = fBitmap;
+    return true;
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 
 SkImage* SkImage::NewRasterCopy(const SkImage::Info& info, const void* pixels, size_t rowBytes) {