Extensions: ChromeExtensionWCO::ReadyToCommitNavigation should call its superclass impl.

r551018 introduced an override for ReadyToCommitNavigation method on
ChromeExtensionWebContentsObserver. However it failed to call its superclass
implementation. Fix it.

BUG=696822

Change-Id: I882c8af072f942e65072fb06e3b2209d2e983c1c
Reviewed-on: https://chromium-review.googlesource.com/1039158Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Commit-Queue: Karan Bhatia <karandeepb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#555533}

chrome/browser/extensions/chrome_extension_web_contents_observer.cc

@@ -173,6 +173,7 @@ void ChromeExtensionWebContentsObserver::ReloadIfTerminated(
 
 void ChromeExtensionWebContentsObserver::ReadyToCommitNavigation(
     content::NavigationHandle* navigation_handle) {
+  ExtensionWebContentsObserver::ReadyToCommitNavigation(navigation_handle);
   const ExtensionRegistry* registry = ExtensionRegistry::Get(
       navigation_handle->GetWebContents()->GetBrowserContext());