Update OnCommit to 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 146 matching lines @@
   // 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
   // reference to it.
   // Note that this does not get called for same page navigations.
-  virtual void OnCommit(content::NavigationHandle* navigation_handle) {}
+  // Observers that return STOP_OBSERVING will not receive any additional
+  // callbacks, and will be deleted after invocation of this method returns.
+  virtual ObservePolicy OnCommit(content::NavigationHandle* navigation_handle);
 
   // OnHidden is triggered when a page leaves the foreground. It does not fire
   // when a foreground page is permanently closed; for that, listen to
   // OnComplete instead.
   virtual void OnHidden() {}
 
   // OnShown is triggered when a page is brought to the foreground. It does not
   // fire when the page first loads; for that, listen for OnStart instead.
   virtual void OnShown() {}
 
@@ skipping 78 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_