Implement a simple image cache for Sky in Dart (no eviction)

sky/engine/core/loader/CanvasImageLoader.cpp

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "sky/engine/config.h"
 #include "sky/engine/core/loader/CanvasImageLoader.h"
 #include "sky/engine/core/painting/CanvasImage.h"
 #include "sky/engine/platform/image-decoders/ImageDecoder.h"
 #include "sky/engine/platform/SharedBuffer.h"
 
 namespace blink {
 
 CanvasImageLoader::CanvasImageLoader(const String& src, PassOwnPtr<ImageLoaderCallback> callback)
   : callback_(callback) {
   // TODO(jackson): Figure out how to determine the proper base URL here
-  url_ = KURL(KURL(), src);
+  KURL url = KURL(KURL(), src);
+  fetcher_ = adoptPtr(new MojoFetcher(this, url));
 }
 
 CanvasImageLoader::~CanvasImageLoader() {
 }
 
-void CanvasImageLoader::load() {
-  fetcher_ = adoptPtr(new MojoFetcher(this, url_));
-}
-
 void CanvasImageLoader::OnReceivedResponse(mojo::URLResponsePtr response) {
   if (response->status_code != 200) {
     callback_->handleEvent(nullptr);
     return;
   }
   buffer_ = SharedBuffer::create();
   drainer_ =
       adoptPtr(new mojo::common::DataPipeDrainer(this, response->body.Pass()));
 }
 
 void CanvasImageLoader::OnDataAvailable(const void* data, size_t num_bytes) {
   buffer_->append(static_cast<const char*>(data), num_bytes);
 }
 
 void CanvasImageLoader::OnDataComplete() {
   OwnPtr<ImageDecoder> decoder =
       ImageDecoder::create(*buffer_.get(), ImageSource::AlphaPremultiplied,
                            ImageSource::GammaAndColorProfileIgnored);
   decoder->setData(buffer_.get(), true);
   if (!decoder->failed() && decoder->frameCount() > 0) {
     RefPtr<CanvasImage> resultImage = CanvasImage::create();
     resultImage->setBitmap(decoder->frameBufferAtIndex(0)->getSkBitmap());
     callback_->handleEvent(resultImage.get());
   } else {
     callback_->handleEvent(nullptr);
   }
 }
 
 }  // namespace blink