Fixes bug where recreating the document element via altering |documentElement...

chrome/browser/extensions/extension_host.cc

Index: chrome/browser/extensions/extension_host.cc
===================================================================
--- chrome/browser/extensions/extension_host.cc	(revision 35457)
+++ chrome/browser/extensions/extension_host.cc	(working copy)
@@ -355,6 +355,11 @@
 }
 
 void ExtensionHost::DocumentAvailableInMainFrame(RenderViewHost* rvh) {
+  // If the document has already been marked as available for this host, then
+  // bail. No need for the redundant setup. http://crbug.com/31170
+  if (document_element_available_)
+    return;
+
   document_element_available_ = true;
   if (is_background_page()) {
     extension_->SetBackgroundPageReady();