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

chrome/common/page_load_metrics/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_COMMON_PAGE_LOAD_METRICS_PAGE_TRACK_DECIDER_H_
 #define CHROME_COMMON_PAGE_LOAD_METRICS_PAGE_TRACK_DECIDER_H_
 
 #include "base/macros.h"
 
 namespace page_load_metrics {
 
 // PageTrackDecider is an interface used to determine whether metrics should be
 // tracked for a given page. This class is used by the core page load metrics
 // tracking infrastructure in both the browser and render processes so policy
 // decisions about which page loads to track are consistent across processes.
 class PageTrackDecider {
  public:
   PageTrackDecider();
   virtual ~PageTrackDecider();
 
   // Whether metrics should be tracked for the current page. This method invokes
   // the pure virtual methods below to decide whether metrics should be tracked.
   bool ShouldTrack();
 
   // Whether the navigation for the current page has committed.
   virtual bool HasCommitted() = 0;
 
-  // Whether the current page's URL is HTTP or HTTPS. Note that the page does
-  // not need to have committed, nor does the URL or hostname of the URL need to
-  // point at a valid web page or host, for this method to return true.
-  virtual bool IsHttpOrHttpsUrl() = 0;
-
   // Whether the current page's URL is for a Chrome new tab page. Note that in
   // some cases the new tab page is served over the network via https.
   virtual bool IsNewTabPageUrl() = 0;
 
+  virtual bool IsAboutBlankUrl() = 0;
+
   // The methods below can only be called if HasCommitted() returns true.
 
   // Whether the current page is a Chrome-generated error page. Example error
   // pages include pages displayed after a network error that did not result in
   // receiving an HTTP/HTTPS response, such as the 'There is no Internet
   // connection' page, which is displayed when the user attempts to navigate
   // without an Internet connection. This method returns false for non-Chrome
   // generated error pages, such as pages with 4xx/5xx response codes. To
   // check whether the current page resulted in a 4xx/5xx error, use
   // IsHTTPErrorPage() instead.
   virtual bool IsChromeErrorPage() = 0;
 
   // Returns the HTTP status code for the current page, or -1 if no status code
   // is available.
   virtual int GetHttpStatusCode() = 0;
 
   // Whether the current page is an HTML or XHTML page.
   virtual bool IsHtmlOrXhtmlPage() = 0;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(PageTrackDecider);
 };
 
 }  // namespace page_load_metrics
 
 #endif  // CHROME_COMMON_PAGE_LOAD_METRICS_PAGE_TRACK_DECIDER_H_