Remove trampoline between threads in SupportedImageTypeValidator.

chrome/browser/image_decoder.h

 // Copyright (c) 2012 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_IMAGE_DECODER_H_
 #define CHROME_BROWSER_IMAGE_DECODER_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 25 matching lines @@
 
   enum ImageCodec {
     DEFAULT_CODEC = 0,  // Uses WebKit image decoding (via WebImage).
     ROBUST_JPEG_CODEC,  // Restrict decoding to robust jpeg codec.
   };
 
   ImageDecoder(Delegate* delegate,
                const std::string& image_data,
                ImageCodec image_codec);
 
-  // Starts image decoding on current thread of |task_runner|.
+  // Starts asynchronous image decoding. Once finished, the callback will be
+  // posted back to |task_runner|.
   void Start(scoped_refptr<base::SequencedTaskRunner> task_runner);
 
   const std::vector<unsigned char>& get_image_data() const {
     return image_data_;
   }
 
   void set_delegate(Delegate* delegate) { delegate_ = delegate; }
 
  private:
   // It's a reference counted object, so destructor is private.
@@ skipping 11 matching lines @@
 
   Delegate* delegate_;
   std::vector<unsigned char> image_data_;
   const ImageCodec image_codec_;
   scoped_refptr<base::SequencedTaskRunner> task_runner_;
 
   DISALLOW_COPY_AND_ASSIGN(ImageDecoder);
 };
 
 #endif  // CHROME_BROWSER_IMAGE_DECODER_H_