Cache the current WebPreferences on RenderViewHostImpl (try #2).

content/browser/renderer_host/render_view_host_impl.h

Index: content/browser/renderer_host/render_view_host_impl.h
diff --git a/content/browser/renderer_host/render_view_host_impl.h b/content/browser/renderer_host/render_view_host_impl.h
index b099a7b280f63bef518c334f79777250201be3dc..4c674a53b9a29311ae4cc27b8976d337a194d32d 100644
--- a/content/browser/renderer_host/render_view_host_impl.h
+++ b/content/browser/renderer_host/render_view_host_impl.h
@@ -204,6 +204,7 @@ class CONTENT_EXPORT RenderViewHostImpl
   virtual WebPreferences GetWebkitPreferences() OVERRIDE;
   virtual void UpdateWebkitPreferences(
       const WebPreferences& prefs) OVERRIDE;
+  virtual void OnWebkitPreferencesChanged() OVERRIDE;
   virtual void GetAudioOutputControllers(
       const GetAudioOutputControllersCallback& callback) const OVERRIDE;
   virtual void SelectWordAroundCaret() OVERRIDE;
@@ -241,7 +242,7 @@ class CONTENT_EXPORT RenderViewHostImpl
   }
 
   // Returns the content specific prefs for this RenderViewHost.
-  WebPreferences GetWebkitPrefs(const GURL& url);
+  WebPreferences ComputeWebkitPrefs(const GURL& url);
 
   // Sends the given navigation message. Use this rather than sending it
   // yourself since this does the internal bookkeeping described below. This
@@ -612,6 +613,13 @@ class CONTENT_EXPORT RenderViewHostImpl
   // True if the current focused element is editable.
   bool is_focused_element_editable_;
 
+  // This is updated every time UpdateWebkitPreferences is called. That method
+  // is in turn called when any of the settings change that the WebPreferences
+  // values depend on.
+  scoped_ptr<WebPreferences> web_preferences_;
+
+  bool updating_web_preferences_;
+
   DISALLOW_COPY_AND_ASSIGN(RenderViewHostImpl);
 };