Revert of Revert[2] of add ImageShader, sharing code with its Bitmap cousin

src/image/SkImage_Generator.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkImage_Base.h"
 #include "SkBitmap.h"
 #include "SkCanvas.h"
@@ skipping 10 matching lines @@
         , fCache(cache) // take ownership
     {}
 
     bool onReadPixels(const SkImageInfo&, void*, size_t, int srcX, int srcY) const override;
     const void* onPeekPixels(SkImageInfo*, size_t* /*rowBytes*/) const override;
     SkData* onRefEncoded() const override;
     bool isOpaque() const override { return fCache->info().isOpaque(); }
     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:
     SkAutoTDelete<SkImageCacherator> fCache;
 
     typedef SkImage_Base INHERITED;
 };
 
 ///////////////////////////////////////////////////////////////////////////////
 
+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 {
     SkBitmap bm;
     if (this->getROPixels(&bm)) {
         return bm.readPixels(dstInfo, dstPixels, dstRB, srcX, srcY);
     }
     return false;
 }
 
 const void* SkImage_Generator::onPeekPixels(SkImageInfo* infoPtr, size_t* rowBytesPtr) const {
@@ skipping 28 matching lines @@
     return surface->newImageSnapshot();
 }
 
 SkImage* SkImage::NewFromGenerator(SkImageGenerator* generator, const SkIRect* subset) {
     SkImageCacherator* cache = SkImageCacherator::NewFromGenerator(generator, subset);
     if (!cache) {
         return nullptr;
     }
     return new SkImage_Generator(cache);
 }