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