Make PageLoadMetricsObserver::OnStart return ObservePolicy

chrome/browser/page_load_metrics/page_load_metrics_observer.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_PAGE_LOAD_METRICS_PAGE_LOAD_METRICS_OBSERVER_H_
 #define CHROME_BROWSER_PAGE_LOAD_METRICS_PAGE_LOAD_METRICS_OBSERVER_H_
 
 #include "base/macros.h"
 #include "base/optional.h"
 #include "chrome/common/page_load_metrics/page_load_timing.h"
@@ skipping 131 matching lines @@
   virtual ~PageLoadMetricsObserver() {}
 
   // The page load started, with the given navigation handle. Note that OnStart
   // is called for same-page navigations. Implementers of OnStart that only want
   // to process non-same-page navigations should also check to see that the page
   // load committed via OnCommit or committed_url in
   // PageLoadExtraInfo. currently_committed_url contains the URL of the
   // committed page load at the time the navigation for navigation_handle was
   // initiated, or the empty URL if there was no committed page load at the time
   // the navigation was initiated.
-  virtual void OnStart(content::NavigationHandle* navigation_handle,
-                       const GURL& currently_committed_url,
-                       bool started_in_foreground) {}
+  virtual ObservePolicy OnStart(content::NavigationHandle* navigation_handle,
+                                const GURL& currently_committed_url,
+                                bool started_in_foreground);
 
   // OnRedirect is triggered when a page load redirects to another URL.
   // The navigation handle holds relevant data for the navigation, but will
   // be destroyed soon after this call. Don't hold a reference to it. This can
   // be called multiple times.
   virtual void OnRedirect(content::NavigationHandle* navigation_handle) {}
 
   // OnCommit is triggered when a page load commits, i.e. when we receive the
   // first data for the request. The navigation handle holds relevant data for
   // the navigation, but will be destroyed soon after this call. Don't hold a
@@ skipping 93 matching lines @@
   // loads that result in downloads or 204s are aborted by the system, and are
   // also included as failed provisional loads.
   virtual void OnFailedProvisionalLoad(
       const FailedProvisionalLoadInfo& failed_provisional_load_info,
       const PageLoadExtraInfo& extra_info) {}
 };
 
 }  // namespace page_load_metrics
 
 #endif  // CHROME_BROWSER_PAGE_LOAD_METRICS_PAGE_LOAD_METRICS_OBSERVER_H_