Cache the current WebPreferences on RenderViewHostImpl.

content/public/browser/render_view_host.h

Index: content/public/browser/render_view_host.h
diff --git a/content/public/browser/render_view_host.h b/content/public/browser/render_view_host.h
index 840be8cb0667364800fa7e94129742a2f4207daa..6347ba322801dfd5e3513c12396e6cffdab72e17 100644
--- a/content/public/browser/render_view_host.h
+++ b/content/public/browser/render_view_host.h
@@ -197,6 +197,10 @@ class CONTENT_EXPORT RenderViewHost : virtual public RenderWidgetHost {
   // Returns the current WebKit preferences.

[jam, 2014/07/21 17:40:33]

nit: now that the behavior of this method changed to return a cached version,
this should be called out in the comment

[chrishtr, 2014/07/21 18:16:07]

Done.

   virtual WebPreferences GetWebkitPreferences() = 0;
 
+  // If any state that affects the webkit preferences changed, this method must
+  // be called. This triggers recomputing preferences.
+  virtual void OnWebkitPreferencesChanged() = 0;
+
   // Passes a list of Webkit preferences to the renderer.
   virtual void UpdateWebkitPreferences(const WebPreferences& prefs) = 0;