Add -[CRWWebViewScrollViewObserver webViewScrollViewWillBeginZooming...]

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

Index: ios/web/public/web_state/ui/crw_web_view_scroll_view_proxy.h
diff --git a/ios/web/public/web_state/ui/crw_web_view_scroll_view_proxy.h b/ios/web/public/web_state/ui/crw_web_view_scroll_view_proxy.h
index d677274f1312063d3418ed855f0515edc86662e3..27294d582547ee791faeba07e7693485333d99b7 100644
--- a/ios/web/public/web_state/ui/crw_web_view_scroll_view_proxy.h
+++ b/ios/web/public/web_state/ui/crw_web_view_scroll_view_proxy.h
@@ -79,6 +79,12 @@
     (CRWWebViewScrollViewProxy*)webViewScrollViewProxy;
 - (void)webViewScrollViewDidResetContentSize:
     (CRWWebViewScrollViewProxy*)webViewScrollViewProxy;
+
+// The equivalent in UIScrollViewDelegate also takes a parameter (UIView*)view,
+// but CRWWebViewScrollViewObserver doesn't expose it for flexibility of future
+// implementation.
+- (void)webViewScrollViewWillBeginZooming:
+    (CRWWebViewScrollViewProxy*)webViewScrollViewProxy;
 @end
 
 // A protocol to be implemented by objects to listen for changes to the