Use extension to show activation message.

content/browser/tab_contents/interstitial_page.cc

Index: content/browser/tab_contents/interstitial_page.cc
diff --git a/content/browser/tab_contents/interstitial_page.cc b/content/browser/tab_contents/interstitial_page.cc
index b81ec28539eecb8931e7171e31cd98af33592bd6..2cd09b8133059283e06d38fa3add68703dc522d1 100644
--- a/content/browser/tab_contents/interstitial_page.cc
+++ b/content/browser/tab_contents/interstitial_page.cc
@@ -19,6 +19,8 @@
 #include "chrome/common/bindings_policy.h"
 #include "chrome/common/dom_storage_common.h"
 #include "chrome/common/net/url_request_context_getter.h"
+#include "chrome/common/page_transition_types.h"
+#include "chrome/common/render_messages_params.h"
 #include "content/browser/browser_thread.h"
 #include "content/browser/renderer_host/render_process_host.h"
 #include "content/browser/renderer_host/render_view_host.h"
@@ -351,6 +353,10 @@ void InterstitialPage::DidNavigate(
     DontProceed();
     return;
   }
+  if (params.transition == PageTransition::AUTO_SUBFRAME) {
+    // No need to handle navigate message from iframe in the interstitial page.
+    return;
+  }
 
   // The RenderViewHost has loaded its contents, we can show it now.
   render_view_host_->view()->Show();