Zero-out crw_web_controller's container view delegate in dealloc.

ios/web/web_state/ui/crw_web_controller.mm

Index: ios/web/web_state/ui/crw_web_controller.mm
diff --git a/ios/web/web_state/ui/crw_web_controller.mm b/ios/web/web_state/ui/crw_web_controller.mm
index 944494a6005ea7c1d5d1072e04c913dfc4307aaa..cb93adeba2a29f6c3333d1e03a1fbefd5c2cdb45 100644
--- a/ios/web/web_state/ui/crw_web_controller.mm
+++ b/ios/web/web_state/ui/crw_web_controller.mm
@@ -1114,6 +1114,7 @@ const NSTimeInterval kSnapshotOverlayTransition = 0.5;
   DCHECK([NSThread isMainThread]);
   DCHECK(_isBeingDestroyed);  // 'close' must have been called already.
   DCHECK(!_webView);
+  [_containerView setDelegate:nil];

[Eugene But (OOO till 7-30), 2016/10/25 18:24:34]

Is this change temporary? If so, could you please add TODO to remove it.
Otherwise could you please add a comment which explains why this is necessary.

   _touchTrackingRecognizer.get().touchTrackingDelegate = nil;
   [[_webViewProxy scrollViewProxy] removeObserver:self];
   [[NSNotificationCenter defaultCenter] removeObserver:self];