Adds metric to help assess last_n impact on tab restores.

chrome/android/java/src/org/chromium/chrome/browser/tab/TabWebContentsObserver.java

 // 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.
 
 package org.chromium.chrome.browser.tab;
 
 import android.os.SystemClock;
 import android.support.annotation.IntDef;
 import android.view.View;
 
@@ skipping 113 matching lines @@
         } else {
             rendererCrashStatus = TAB_RENDERER_CRASH_STATUS_SHOWN_IN_FOREGROUND_APP;
             mTab.showSadTab();
             // This is necessary to correlate histogram data with stability counts.
             UmaSessionStats.logRendererCrash();
         }
         RecordHistogram.recordEnumeratedHistogram(
                 "Tab.RendererCrashStatus", rendererCrashStatus, TAB_RENDERER_CRASH_STATUS_MAX);
 
         mTab.handleTabCrash();
-
-        boolean sadTabShown = mTab.isShowingSadTab();
-        RewindableIterator<TabObserver> observers = mTab.getTabObservers();
-        while (observers.hasNext()) {
-            observers.next().onCrash(mTab, sadTabShown);
-        }
     }
 
     @Override
     public void navigationEntryCommitted() {
         if (mTab.getNativePage() != null) {
             mTab.pushNativePageStateToNavigationEntry();
         }
     }
 
     @Override
@@ skipping 155 matching lines @@
         }
     }
 
     @Override
     public void destroy() {
         MediaCaptureNotificationService.updateMediaNotificationForTab(
                 mTab.getApplicationContext(), mTab.getId(), 0, mTab.getUrl());
         super.destroy();
     }
 }