Revert of Revert[2] of 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 1c1b26337178aa1965058a8fb0121ef73fd85c25..765234fa0c0e1757487220b99f1d1b2fdfc39706 100644
--- a/src/image/SkImage_Generator.cpp
+++ b/src/image/SkImage_Generator.cpp
@@ -28,6 +28,11 @@
     SkImage* onNewSubset(const SkIRect&) const override;
     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:
@@ -37,6 +42,17 @@
 };
 
 ///////////////////////////////////////////////////////////////////////////////
+
+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;
+}
 
 bool SkImage_Generator::onReadPixels(const SkImageInfo& dstInfo, void* dstPixels, size_t dstRB,
                                      int srcX, int srcY) const {