[Large Icon Service] Move icon resizing into worker thread.

components/favicon/core/large_icon_service.h

-// Copyright (c) 2015 The Chromium Authors. All rights reserved.
+// 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.
 
 #ifndef COMPONENTS_FAVICON_CORE_LARGE_ICON_SERVICE_H_
 #define COMPONENTS_FAVICON_CORE_LARGE_ICON_SERVICE_H_
 
 #include <vector>
 
+#include "base/memory/ref_counted.h"
+#include "base/memory/scoped_ptr.h"
 #include "base/task/cancelable_task_tracker.h"
 #include "components/favicon_base/favicon_callback.h"
+#include "components/favicon_base/favicon_types.h"
 #include "components/keyed_service/core/keyed_service.h"
 
 class GURL;
 
-namespace favicon_base {
-struct FaviconRawBitmapResult;
-}
-
 namespace favicon {
 
 class FaviconService;
+class LargeIconResult;
 
 // The large icon service provides methods to access large icons. It relies on
 // the favicon service.
 class LargeIconService : public KeyedService {
  public:
+  struct Session : base::RefCountedThreadSafe<Session> {
+   public:
+    int desired_size_in_pixel;
+    favicon_base::LargeIconCallback callback;
+    base::CancelableTaskTracker* tracker;
+    favicon_base::FaviconRawBitmapResult bitmap_result;
+    scoped_ptr<favicon_base::LargeIconResult> result;
+  };
+
   explicit LargeIconService(FaviconService* favicon_service);
 
   ~LargeIconService() override;
 
   // Requests the best large icon for the page at |page_url| given the requested
   // |desired_size_in_pixel|. If no good large icon can be found, returns the
   // fallback style to use, for which the background is set to the dominant
   // color of a smaller icon when one is available. This function returns the
   // style of the fallback icon rather than the rendered version so that clients
-  // can render the icon themselves.
+  // can render the icon themselves. This run on the UI thread.
   base::CancelableTaskTracker::TaskId GetLargeIconOrFallbackStyle(
     const GURL& page_url,
     int desired_size_in_pixel,
     const favicon_base::LargeIconCallback& callback,
     base::CancelableTaskTracker* tracker);
 
- private:
   // Resizes |bitmap_result| to |desired_size_in_pixel|x|desired_size_in_pixel|.
   // Stores the resized bitmap data in |resized_bitmap_result| and returns true
-  // if successful.
-  bool ResizeLargeIconIfValid(
-      int desired_size_in_pixel,
-      const favicon_base::FaviconRawBitmapResult& bitmap_result,
-      favicon_base::FaviconRawBitmapResult* resized_bitmap_result);
+  // if successful. This runs on a background thread.
+  static bool ResizeLargeIconIfValid(
+    int desired_size_in_pixel,
+    const favicon_base::FaviconRawBitmapResult& bitmap_result,
+    favicon_base::FaviconRawBitmapResult* resized_bitmap_result);
 
-  // Intermediate callback for GetLargeIconOrFallbackStyle(). Tries to resize
-  // |bitmap_result| and pass the output to |callback|. If that does not work,
-  // computes the icon fallback style and uses it to invoke |callback|.
-  void RunLargeIconCallback(
-      const favicon_base::LargeIconCallback& callback,
-      int desired_size_in_pixel,
+ private:
+  // Intermediate callback for GetLargeIconOrFallbackStyle(). This runs on the
+  // UI thread, and should not perform complex image operations.
+  void OnIconLookupComplete(
+      scoped_refptr<Session> session,
       const favicon_base::FaviconRawBitmapResult& bitmap_result);
 
+  // Tries to resize |bitmap_result| and pass the output to |callback|. If that
+  // does not work, computes the icon fallback style and uses it to invoke
+  // |callback|. The runs on a background thread since image resizing and
+  // dominant color extraction can be expensive.
+  void ProcessIconOnBackgroundThread(scoped_refptr<Session> session);
+
+  // Callback to be invoked when ProcessIconOnBackgroundThread() is ready. This
+  // runs on the UI thread.
+  void OnIconProcessingComplete(scoped_refptr<Session> session);
+
   FaviconService* favicon_service_;
 
   // A pre-populated list of the types of icon files to consider when looking
   // for large icons. This is an optimization over populating an icon type
   // vector on each request.
   std::vector<int> large_icon_types_;
 
   DISALLOW_COPY_AND_ASSIGN(LargeIconService);
 };
 
 }  // namespace favicon
 
 #endif  // COMPONENTS_FAVICON_CORE_LARGE_ICON_SERVICE_H_