Make image_decoder a Leaky LazyInstance

chrome/browser/bitmap_fetcher/bitmap_fetcher.h

 // Copyright 2014 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.
 
 #ifndef CHROME_BROWSER_BITMAP_FETCHER_BITMAP_FETCHER_H_
 #define CHROME_BROWSER_BITMAP_FETCHER_BITMAP_FETCHER_H_
 
 #include "base/memory/scoped_ptr.h"
 #include "chrome/browser/bitmap_fetcher/bitmap_fetcher_delegate.h"
 #include "chrome/browser/image_decoder.h"
 #include "net/url_request/url_fetcher_delegate.h"
 #include "net/url_request/url_request.h"
 #include "third_party/skia/include/core/SkBitmap.h"
 #include "url/gurl.h"
 
 namespace net {
 class URLFetcher;
 class URLRequestContextGetter;
 }  // namespace net
 
 namespace chrome {
 
 // Asynchrounously fetches an image from the given URL and returns the
-// decoded Bitmap to the provided BitmapFetcherDelegate.
+// decoded Bitmap to the provided BitmapFetcherDelegate. This class is
+// deprecated and will be removed once crbug.com/<TODO(twellington): fill
+// this in once deprecation is approved and bug is created> is resolved. Use
+// BitmapBatchFetcher instead.

[Nico, 2015/02/18 20:59:17]

To me, it seems like a better strategy to me to swap out the implementation of
this class transparently instead of changing all clients to use the new class –
they should be mostly interface-compatible right? That's what abstractions are
for, after all.

Maybe the implementation could pick one of the two behaviors based on a flag,
then you can roll this out behind a flag and don't need a new class at all – and
once you're happy with how the flag performs, you can turn it on by default and
rip out the old code.

 class BitmapFetcher : public net::URLFetcherDelegate,
                       public ImageDecoder::Delegate {
  public:
   BitmapFetcher(const GURL& url, BitmapFetcherDelegate* delegate);
   ~BitmapFetcher() override;
 
   const GURL& url() const { return url_; }
 
   // Start fetching the URL with the fetcher. The delegate is notified
   // asynchronously when done.  Start may be called more than once in some
@@ skipping 38 matching lines @@
   scoped_refptr<ImageDecoder> image_decoder_;
   const GURL url_;
   BitmapFetcherDelegate* const delegate_;
 
   DISALLOW_COPY_AND_ASSIGN(BitmapFetcher);
 };
 
 }  // namespace chrome
 
 #endif  // CHROME_BROWSER_BITMAP_FETCHER_BITMAP_FETCHER_H_