[Favicon] Add new fallback icon rendering flow.

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 "components/favicon_base/fallback_icon_service.h"
+#include "content/public/browser/url_data_source.h"
+
+// FallbackIconSource is the gateway between network-level chrome:
+// requests for fallback icons and the backend that renders these.
+//
+// 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.
+//  'bc'
+//    Color in RRGGBBAA, RRGGBB, or RGB hex format, to specify the fallback
+//    icon's background color.
+//  'tc'
+//    Color in RRGGBBAA, RRGGBB, or RGB hex format, to specify the fallback
+//    icon's text color.
+//  'fsr'
+//    Number in [0.0, 1.0] to specify the fallback icon's font size (pixels)
+//    as a ratio to the icon's size.
+//  'r'
+//    Number in [0.0, 1.0] to specify the fallback icon's roundness.
+//    0.0 specifies a square icon; 1.0 specifies a circle icon; intermediate
+//    values specify a rounded square icon.
+//  'url'
+//    String to specify the page URL of the fallback icon.
+//
+//  Example: chrome://fallback-icon/32,fff,000,0.5,1.0/http://www.google.com/
+//    This requests a 32x32 fallback icon for http://www.google.com, using
+//    #fff 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();
+
+  ~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:
+  // Sends the default fallback icon.
+  void SendDefaultResponse(
+      const content::URLDataSource::GotDataCallback& callback);
+
+  favicon_base::FallbackIconService fallback_icon_service_;
+
+  DISALLOW_COPY_AND_ASSIGN(FallbackIconSource);
+};
+
+#endif  // CHROME_BROWSER_UI_WEBUI_FALLBACK_ICON_SOURCE_H_