Fix top renderer crash. Extension can go away before Context. Duh.

chrome/renderer/extensions/chrome_v8_context.h

Index: chrome/renderer/extensions/chrome_v8_context.h
diff --git a/chrome/renderer/extensions/chrome_v8_context.h b/chrome/renderer/extensions/chrome_v8_context.h
index e49b638fe08dbbdd4702e8e248f069ee4e11297d..479568805ebda9dd00a14dcb8aa9d38a50d3c8fc 100644
--- a/chrome/renderer/extensions/chrome_v8_context.h
+++ b/chrome/renderer/extensions/chrome_v8_context.h
@@ -39,7 +39,7 @@ class ChromeV8Context {
   }
 
   const Extension* extension() const {
-    return extension_;
+    return extension_.get();
   }
 
   WebKit::WebFrame* web_frame() const {
@@ -114,7 +114,7 @@ class ChromeV8Context {
 
   // The extension associated with this context, or NULL if there is none. This
   // might be a hosted app in the case that this context is hosting a web URL.
-  const Extension* extension_;
+  scoped_refptr<const Extension> extension_;
 
   // The type of context.
   extensions::Feature::Context context_type_;