Move histograms and supporting code that don't belong in content out.

content/public/browser/web_contents_observer.h

Index: content/public/browser/web_contents_observer.h
diff --git a/content/public/browser/web_contents_observer.h b/content/public/browser/web_contents_observer.h
index 0a011719f6337f509c9dba5922fa3d3640c12326..d7490e7283c03f9ade9f2f590d6dd5eed5e36288 100644
--- a/content/public/browser/web_contents_observer.h
+++ b/content/public/browser/web_contents_observer.h
@@ -259,6 +259,12 @@ class CONTENT_EXPORT WebContentsObserver : public IPC::Listener,
   // Invoked before a form repost warning is shown.
   virtual void BeforeFormRepostWarningShow() {}
 
+  // Invoked when the beforeunload handler fires. The time is from the renderer.
+  virtual void BeforeUnloadFired(const base::TimeTicks& proceed_time) {}
+
+  // Invoked when a user cancels a before unload dialog.
+  virtual void BeforeUnloadDialogCancelled() {}
+
   // IPC::Listener implementation.
   virtual bool OnMessageReceived(const IPC::Message& message) OVERRIDE;