Add CRWNativeContent willBeDismissed.

ios/web/public/web_state/ui/crw_native_content.h

Index: ios/web/public/web_state/ui/crw_native_content.h
diff --git a/ios/web/public/web_state/ui/crw_native_content.h b/ios/web/public/web_state/ui/crw_native_content.h
index 994ba6d2fd8c7b8228d1f73b61e69780db38376e..cc880295600a009d86c64204669c5ef008de8276 100644
--- a/ios/web/public/web_state/ui/crw_native_content.h
+++ b/ios/web/public/web_state/ui/crw_native_content.h
@@ -85,6 +85,9 @@
 // Called when a snapshot of the content will be taken.
 - (void)willUpdateSnapshot;
 
+// Called when a navigation is triggered from this nativeContent.

[Eugene But (OOO till 7-30), 2016/12/21 15:26:35]

nit: Is this called on reload? Should this comment be "Notifies the
CRWNativeContent that it will be removed from superview"?

[Olivier, 2016/12/21 15:41:11]

It is called on reload.
I will change the comment.

[Olivier, 2016/12/21 15:51:36]

Actually it is not called on reload.

[Olivier, 2016/12/21 15:51:36]

Done.

[Eugene But (OOO till 7-30), 2016/12/21 16:11:10]

With your new comment no one will expect this to be called on reload, so this is
fine :)

+- (void)willBeDismissed;
+
 // The URL that will be displayed to the user when presenting this native
 // content.
 - (GURL)virtualURL;