[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 base {
+class TaskRunner;
 }
 
 namespace favicon {
 
 class FaviconService;
 
 // The large icon service provides methods to access large icons. It relies on
 // the favicon service.
 class LargeIconService : public KeyedService {
  public:
+  // Tracks the states of a request session for LargeIconService, and manages
+  // the callback chain on different threads.
+  class Session : public base::RefCountedThreadSafe<Session> {

[pkotwicz, 2015/05/11 14:35:08]

I wonder whether:
- This class can be called LargeIconProcessor
- Session::OnIconLookupComplete() can be renamed to LargeIconProcessor::Run()
- Live in the anonymous namespace
- Not be ref counted (Deletes itself when it is done its processing) e.g.
UpdateShortcutWorker does this. I think that the lifetime of Session is pretty
subtle

[huangs, 2015/05/11 15:20:39]

- Renamed to LargeIconWorker.
- Kept Session::OnIconLookupComplete() name per offline discussion.
- Moved to anonymous namespace, and updated #include.
- Kept ref counted, per discussion.

+   public:
+    Session(int min_source_size_in_pixel,
+            int desired_size_in_pixel,
+            favicon_base::LargeIconCallback callback,
+            scoped_refptr<base::TaskRunner> background_task_runner,
+            base::CancelableTaskTracker* tracker);
+
+    // Must run on the owner (UI) thread in production.
+    // Intermediate callback for GetLargeIconOrFallbackStyle(). Invokes
+    // ProcessIconOnBackgroundThread() so we do not perform complex image
+    // operations on the UI thread.
+    void OnIconLookupComplete(
+        const favicon_base::FaviconRawBitmapResult& bitmap_result);
+
+   private:
+    friend class base::RefCountedThreadSafe<Session>;
+    ~Session();
+
+    // Must run on a background thread in production.
+    // 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|. This must be run on a background thread because image
+    // resizing and dominant color extraction can be expensive.
+    void ProcessIconOnBackgroundThread();
+
+    // Must run on a background thread in production.
+    // If |bitmap_result| is square and large enough (>= |min_source_in_pixel|),
+    // resizes it to |desired_size_in_pixel| (but if |desired_size_in_pixel| is
+    // 0 then don't resize). If successful, stores the resulting bitmap data
+    // into |resized_bitmap_result| and returns true.
+    static bool ResizeLargeIconOnBackgroundThreadIfValid(
+        int min_source_size_in_pixel,
+        int desired_size_in_pixel,
+        const favicon_base::FaviconRawBitmapResult& bitmap_result,
+        favicon_base::FaviconRawBitmapResult* resized_bitmap_result);
+
+    // Must run on the owner (UI) thread in production.
+    // Invoked when ProcessIconOnBackgroundThread() is done.
+    void OnIconProcessingComplete();
+
+    int min_source_size_in_pixel_;
+    int desired_size_in_pixel_;
+    favicon_base::LargeIconCallback callback_;
+    scoped_refptr<base::TaskRunner> background_task_runner_;
+    scoped_refptr<base::TaskRunner> caller_task_runner_;
+    base::CancelableTaskTracker* tracker_;
+    favicon_base::FaviconRawBitmapResult bitmap_result_;
+    scoped_ptr<favicon_base::LargeIconResult> result_;
+
+    DISALLOW_COPY_AND_ASSIGN(Session);
+  };
+
   explicit LargeIconService(FaviconService* favicon_service);
 
   ~LargeIconService() override;
 
   // Requests the best large icon for the page at |page_url|.
   // Case 1. An icon exists whose size is >= |min_source_size_in_pixel|:
   // - If |desired_size_in_pixel| == 0: returns icon as is.
   // - Else: returns the icon resized to |desired_size_in_pixel|.
   // Case 2. An icon exists whose size is < |min_source_size_in_pixel|:
   // - Extracts dominant color of smaller image, returns a fallback icon style
   //   that has a matching background.
   // Case 3. No icon exists.
   // - Returns the default fallback icon style.
   // For cases 2 and 3, this function returns the style of the fallback icon
   // instead of rendering an icon so clients can render the icon themselves.
   base::CancelableTaskTracker::TaskId GetLargeIconOrFallbackStyle(
     const GURL& page_url,
     int min_source_size_in_pixel,
     int desired_size_in_pixel,
     const favicon_base::LargeIconCallback& callback,
     base::CancelableTaskTracker* tracker);
 
+  // Returns TaskRunner used to execute background task.
+  virtual scoped_refptr<base::TaskRunner> GetBackgroundTaskRunner();
+
  private:
   // For testing.
   friend class TestLargeIconService;
 
-  // 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 min_source_size_in_pixel,
-      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 min_source_size_in_pixel,
-      int desired_size_in_pixel,
-      const favicon_base::FaviconRawBitmapResult& bitmap_result);
-
   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.
+  // A pre-populated list of icon types 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_