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 e2a97648b6317adaadf1d23a78f26b0530f14a46..6d69007015da6c6fe0248968ff397d837a250c51 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(

[boliu, 2014/08/06 16:52:35]

I think this should be removed from the public content api now? (Didn't actually
check if all usage is removed)

[chrishtr, 2014/08/06 17:00:51]

There are still call sites (some in this CL). This is the way to explicitly
update the preferences.
See for example voice_search_tab_helper.cc.

       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
@@ -607,6 +608,13 @@ 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);
 };