[page_load_metrics] Add support for chrome:// urls and add extensions observer

chrome/renderer/page_load_metrics/renderer_page_track_decider.h

 // Copyright 2016 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_RENDERER_PAGE_LOAD_METRICS_RENDERER_PAGE_TRACK_DECIDER_H_
 #define CHROME_RENDERER_PAGE_LOAD_METRICS_RENDERER_PAGE_TRACK_DECIDER_H_
 
 #include "base/macros.h"
 #include "chrome/common/page_load_metrics/page_track_decider.h"
 
 namespace blink {
 class WebDocument;
 class WebDataSource;
 }  // namespace blink
 
 namespace page_load_metrics {
 
 class RendererPageTrackDecider : public PageTrackDecider {
  public:
   // document and data_source are not owned by RendererPageTrackDecider,
   // and must outlive the RendererPageTrackDecider.
   RendererPageTrackDecider(const blink::WebDocument* document,
                            const blink::WebDataSource* data_source);
   ~RendererPageTrackDecider() override;
 
   bool HasCommitted() override;
-  bool IsHttpOrHttpsUrl() override;
   bool IsNewTabPageUrl() override;
+  bool IsAboutBlankUrl() override;
   bool IsChromeErrorPage() override;
   bool IsHtmlOrXhtmlPage() override;
   int GetHttpStatusCode() override;
 
  private:
   const blink::WebDocument* const document_;
   const blink::WebDataSource* const data_source_;
 
   DISALLOW_COPY_AND_ASSIGN(RendererPageTrackDecider);
 };
 
 }  // namespace page_load_metrics
 
 #endif  // CHROME_RENDERER_PAGE_LOAD_METRICS_RENDERER_PAGE_TRACK_DECIDER_H_