Add the method isOpaque() to SkImage

src/image/SkImage_Gpu.cpp

Index: src/image/SkImage_Gpu.cpp
diff --git a/src/image/SkImage_Gpu.cpp b/src/image/SkImage_Gpu.cpp
index 0918412e83c1decbb2bad6e9d26dc8501d73ce55..d98a5367a699cb33bf9b09e05fd2a5b7f04395b7 100644
--- a/src/image/SkImage_Gpu.cpp
+++ b/src/image/SkImage_Gpu.cpp
@@ -31,6 +31,9 @@ public:
     virtual SkShader* onNewShader(SkShader::TileMode,
                                   SkShader::TileMode,
                                   const SkMatrix* localMatrix) const SK_OVERRIDE;
+
+    virtual bool isOpaque() const SK_OVERRIDE;
+
 private:
     SkBitmap    fBitmap;
 
@@ -72,6 +75,10 @@ bool SkImage_Gpu::getROPixels(SkBitmap* dst) const {
     return fBitmap.copyTo(dst, kN32_SkColorType);
 }
 
+bool SkImage_Gpu::isOpaque() const {
+    return fBitmap.isOpaque();
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 
 SkImage* SkImage::NewTexture(const SkBitmap& bitmap) {