Fix crash in StaticHTMLNativeContent when deallocating WKWebView on iOS9

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 6db54aca76abce7987e5d72abb308fd04cd71d62..cc311568aa085529b38bc76e0ce2e8e674f0c426 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
@@ -146,6 +146,9 @@
 }
 
 - (void)dealloc {
+  if ([_nativeController respondsToSelector:@selector(willBeDismissed)]) {
+    [_nativeController willBeDismissed];

[Eugene But (OOO till 7-30), 2017/01/04 21:24:38]

Calling |willBeDismissed| from dealloc does not seems to be correct either.  How
about calling |[[self scrollView] setDelegate:nil];| from
|StaticHtmlNativeContent dealloc|? Setting delegate to nil twice should not be
an issue.

[Olivier, 2017/01/06 10:03:24]

Done.

+  }
   self.contentViewProxy.contentView = nil;
   [super dealloc];
 }