Add the method isOpaque() 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 a1cd602a0733c91c782186338acaf191c28f2fea..a7e4e009e5c2fd2d9b3a1f58457e45b116fc5b6f 100644
--- a/src/image/SkImage_Raster.cpp
+++ b/src/image/SkImage_Raster.cpp
@@ -70,6 +70,8 @@ public:
                                   SkShader::TileMode,
                                   const SkMatrix* localMatrix) const SK_OVERRIDE;
 
+    virtual bool isOpaque() const SK_OVERRIDE;
+
     SkImage_Raster(const SkBitmap& bm)
         : INHERITED(bm.width(), bm.height())
         , fBitmap(bm) {}
@@ -219,3 +221,7 @@ SkImage* SkNewImageFromPixelRef(const SkImageInfo& info, SkPixelRef* pr,
 SkPixelRef* SkBitmapImageGetPixelRef(SkImage* image) {
     return ((SkImage_Raster*)image)->getPixelRef();
 }
+
+bool SkImage_Raster::isOpaque() const {
+    return fBitmap.isOpaque();
+}