Add the method isOpaque() to SkImage

src/image/SkImage_Codec.cpp

Index: src/image/SkImage_Codec.cpp
diff --git a/src/image/SkImage_Codec.cpp b/src/image/SkImage_Codec.cpp
index 21c844d01dd331b0f4235f215fc11ad494fb84bf..0b14216a064d9c6d81670f418b25692b58a9c8bf 100644
--- a/src/image/SkImage_Codec.cpp
+++ b/src/image/SkImage_Codec.cpp
@@ -22,6 +22,8 @@ public:
     virtual void onDrawRectToRect(SkCanvas*, const SkRect*, const SkRect&,
                                   const SkPaint*) const SK_OVERRIDE;
 
+    virtual bool isOpaque() const SK_OVERRIDE;
+
 private:
     SkData*     fEncodedData;
     SkBitmap    fBitmap;
@@ -78,3 +80,8 @@ SkImage* SkImage::NewEncodedData(SkData* data) {
 
     return SkNEW_ARGS(SkImage_Codec, (data, bitmap.width(), bitmap.height()));
 }
+
+
+bool SkImage_Codec::isOpaque() const {
+    return fBitmap.isOpaque();
+}