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

ios/web/web_state/ui/crw_web_controller_container_view.mm

Index: ios/web/web_state/ui/crw_web_controller_container_view.mm
diff --git a/ios/web/web_state/ui/crw_web_controller_container_view.mm b/ios/web/web_state/ui/crw_web_controller_container_view.mm
index 754d9e8b814f4d013b8d1d24e9f24cf48d3314e0..25e31bdead7566ca9822665fe69d06cb203c3764 100644
--- a/ios/web/web_state/ui/crw_web_controller_container_view.mm
+++ b/ios/web/web_state/ui/crw_web_controller_container_view.mm
@@ -212,6 +212,14 @@
                                UIEdgeInsetsMake(headerHeight, 0, 0, 0));
 }
 
+- (id<CRWWebControllerContainerViewDelegate>)delegate {
+  return _delegate.get();
+}
+
+- (void)setDelegate:(id<CRWWebControllerContainerViewDelegate>)delegate {
+  _delegate.reset(delegate);
+}
+
 #pragma mark Layout
 
 - (void)layoutSubviews {