Have ExtensionHost use TabContents instead of RenderViewHost. Try #2. The first

content/browser/tab_contents/tab_contents_observer.cc

Index: content/browser/tab_contents/tab_contents_observer.cc
diff --git a/content/browser/tab_contents/tab_contents_observer.cc b/content/browser/tab_contents/tab_contents_observer.cc
index 42d6fbe83506478bc88ab3c1b7a26eb3c7951f6c..3c1981a0076994df371a714b087b1add65b59a9c 100644
--- a/content/browser/tab_contents/tab_contents_observer.cc
+++ b/content/browser/tab_contents/tab_contents_observer.cc
@@ -63,6 +63,9 @@ void TabContentsObserver::DidFailProvisionalLoad(
     const string16& error_description) {
 }
 
+void TabContentsObserver::DocumentAvailableInMainFrame() {
+}
+
 void TabContentsObserver::DocumentLoadedInFrame(int64 frame_id) {
 }