Add default fonts for extensions

extensions/renderer/dispatcher.h

Index: extensions/renderer/dispatcher.h
diff --git a/extensions/renderer/dispatcher.h b/extensions/renderer/dispatcher.h
index e92463f9c762b9fbdf07481a317dee65a0966fc3..e38a85ecc14c07e73a1a12fe8cf613d619c30eda 100644
--- a/extensions/renderer/dispatcher.h
+++ b/extensions/renderer/dispatcher.h
@@ -214,6 +214,9 @@ class Dispatcher : public content::RenderProcessObserver,
   // Returns whether the current renderer hosts a platform app.
   bool IsWithinPlatformApp();
 
+  // Returns whether the current renderer hosts an extension.
+  bool IsWithinExtension();
+
   bool IsSandboxedPage(const GURL& url) const;
 
   // Returns the Feature::Context type of context for a JavaScript context.