[ios] Fix clean shutdown of Chrome on iOS.

ios/chrome/app/main_controller.mm

 // Copyright 2012 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.
 
 #import "ios/chrome/app/main_controller.h"
 
 #include <memory>
 #include <string>
 
 #import <CoreSpotlight/CoreSpotlight.h>
@@ skipping 935 matching lines @@
              afterDelay:delay];
 }
 
 - (void)activateFirstUserActionRecorderWithBackgroundTime:
     (NSTimeInterval)backgroundTime {
   base::TimeDelta delta = base::TimeDelta::FromSeconds(backgroundTime);
   _firstUserActionRecorder.reset(new FirstUserActionRecorder(delta));
 }
 
 - (void)stopChromeMain {
+  _spotlightManager.reset();

[rohitrao (ping after 24h), 2017/05/16 16:41:02]

There's no guarantee that this call will destroy the spotlight manager.  Is that
something we should handle?

+  _browserViewWrangler.reset();

[sdefresne, 2017/05/16 16:44:40]

There is no guarantee that this will destroy _browserViewWrangler either :-)

   _chromeMain.reset();
 }
 
 - (BOOL)isTabSwitcherActive {
   return _tabSwitcherIsActive;
 }
 
 #pragma mark - BrowserViewInformation implementation.
 
 - (void)haltAllTabs {
@@ skipping 1658 matching lines @@
   };
 
   callbackCounter->IncrementCount();
   [self removeBrowsingDataFromBrowserState:_mainBrowserState
                                       mask:removeAllMask
                                 timePeriod:browsing_data::TimePeriod::ALL_TIME
                          completionHandler:decrementCallbackCounterCount];
 }
 
 @end