Fix crash in StaticHTMLNativeContent when deallocating WKWebView on iOS9

ios/chrome/browser/ui/static_content/static_html_native_content.mm

Index: ios/chrome/browser/ui/static_content/static_html_native_content.mm
diff --git a/ios/chrome/browser/ui/static_content/static_html_native_content.mm b/ios/chrome/browser/ui/static_content/static_html_native_content.mm
index bfaa5a8905ef033758733bc89b46719e8296ef61..af1aebd82891a7eeaa9a4d68530280131fa7a8a0 100644
--- a/ios/chrome/browser/ui/static_content/static_html_native_content.mm
+++ b/ios/chrome/browser/ui/static_content/static_html_native_content.mm
@@ -85,11 +85,16 @@
 - (void)setOverscrollActionsController:
     (OverscrollActionsController*)controller {
   _overscrollActionsController.reset([controller retain]);
+  [[self scrollView] setDelegate:controller];
 }
 
 #pragma mark -
 #pragma mark CRWNativeContent implementation
 
+- (void)willBeDismissed {
+  [[self scrollView] setDelegate:nil];
+}
+
 - (void)close {
   [_overscrollActionsController invalidate];
 }