[Fallback Icons] Refactor FallbackIconService to be a BrowserContext-level singleton

chrome/browser/ui/webui/fallback_icon_source.h

 // 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 CHROME_BROWSER_UI_WEBUI_FALLBACK_ICON_SOURCE_H_
 #define CHROME_BROWSER_UI_WEBUI_FALLBACK_ICON_SOURCE_H_
 
+#include <string>
+
 #include "base/memory/scoped_ptr.h"
-#include "components/favicon/core/fallback_icon_service.h"
 #include "content/public/browser/url_data_source.h"
 
+class FallbackIconService;
+class GURL;
+
+namespace favicon_base {
+struct FallbackIconStyle;
+}
+
 // FallbackIconSource services explicit chrome:// requests for fallback icons.
 //
 // Format:
 //   chrome://fallback-icon/size,bc,tc,fsr,r/url
 // All of the parameters except for the url are optional. However, the order of
 // the parameters is not interchangeable, and all "," must be in place.
 //
 // Parameter:
 //  'size'
 //    Positive integer to specify the fallback icon's size in pixels.
@@ skipping 12 matching lines @@
 //    values specify a rounded square icon.
 //  'url'
 //    String to specify the page URL of the fallback icon.
 //
 //  Example: chrome://fallback-icon/32,red,#000,0.5,1.0/http://www.google.com/
 //    This requests a 32x32 fallback icon for http://www.google.com, using
 //    red as the background color, #000 as the text color, with font size of
 //    32 * 0.5 = 16, and the icon's background shape is a circle.
 class FallbackIconSource : public content::URLDataSource {
  public:
-  FallbackIconSource();
+  // |fallback_icon_service| is owned by caller, and may be null.
+  explicit FallbackIconSource(FallbackIconService* fallback_icon_service);
 
   ~FallbackIconSource() override;
 
   // content::URLDataSource implementation.
   std::string GetSource() const override;
   void StartDataRequest(
       const std::string& path,
       int render_process_id,
       int render_frame_id,
       const content::URLDataSource::GotDataCallback& callback) override;
   std::string GetMimeType(const std::string&) const override;
   bool ShouldReplaceExistingSource() const override;
   bool ShouldServiceRequest(const net::URLRequest* request) const override;
 
  private:
+  void SendFallbackIconHelper(
+      const GURL& url,
+      int size_in_pixels,
+      const favicon_base::FallbackIconStyle& style,
+      const content::URLDataSource::GotDataCallback& callback);
+
   // Sends the default fallback icon.
   void SendDefaultResponse(
       const content::URLDataSource::GotDataCallback& callback);
 
-  scoped_ptr<FallbackIconService> fallback_icon_service_;
+  FallbackIconService* fallback_icon_service_;
 
   DISALLOW_COPY_AND_ASSIGN(FallbackIconSource);
 };
 
 #endif  // CHROME_BROWSER_UI_WEBUI_FALLBACK_ICON_SOURCE_H_