add ImageShader, sharing code with its Bitmap cousin

src/image/SkImage_Generator.cpp

Index: src/image/SkImage_Generator.cpp
diff --git a/src/image/SkImage_Generator.cpp b/src/image/SkImage_Generator.cpp
index 0f1fa3692c8e3dd7a88b46acdc74642555a16e54..f0bf7e364144db8b9106fe1223d176d41017d281 100644
--- a/src/image/SkImage_Generator.cpp
+++ b/src/image/SkImage_Generator.cpp
@@ -28,11 +28,6 @@ public:
 
     bool getROPixels(SkBitmap*) const override;
     GrTexture* asTextureRef(GrContext*, SkImageUsageType) const override;
-
-    SkShader* onNewShader(SkShader::TileMode,
-                          SkShader::TileMode,
-                          const SkMatrix* localMatrix) const override;
-
     bool onIsLazyGenerated() const override { return true; }
 
 private:
@@ -43,17 +38,6 @@ private:
 
 ///////////////////////////////////////////////////////////////////////////////
 
-SkShader* SkImage_Generator::onNewShader(SkShader::TileMode tileX, SkShader::TileMode tileY,
-                                         const SkMatrix* localMatrix) const {
-    // TODO: need a native Shader that takes Cacherator (or this image) so we can natively return
-    // textures as output from the shader.
-    SkBitmap bm;
-    if (this->getROPixels(&bm)) {
-        return SkShader::CreateBitmapShader(bm, tileX, tileY, localMatrix);
-    }
-    return nullptr;
-}
-
 SkSurface* SkImage_Generator::onNewSurface(const SkImageInfo& info,
                                            const SkSurfaceProps& props) const {
     return SkSurface::NewRaster(info, &props);