Split ExtensionMessageFilter up into a UI thread part and an IO thread part.

chrome/browser/extensions/chrome_content_browser_client_extensions_part.cc

Index: chrome/browser/extensions/chrome_content_browser_client_extensions_part.cc
diff --git a/chrome/browser/extensions/chrome_content_browser_client_extensions_part.cc b/chrome/browser/extensions/chrome_content_browser_client_extensions_part.cc
index 13c274f961d9717eaadb97513964483b5c2acb80..67e633d0e14052f7a200dcf48a6b84db67905f09 100644
--- a/chrome/browser/extensions/chrome_content_browser_client_extensions_part.cc
+++ b/chrome/browser/extensions/chrome_content_browser_client_extensions_part.cc
@@ -36,6 +36,7 @@
 #include "extensions/browser/extension_system.h"
 #include "extensions/browser/guest_view/guest_view_message_filter.h"
 #include "extensions/browser/info_map.h"
+#include "extensions/browser/io_thread_extension_message_filter.h"
 #include "extensions/browser/view_type_utils.h"
 #include "extensions/common/constants.h"
 #include "extensions/common/manifest_handlers/background_info.h"
@@ -393,6 +394,7 @@ void ChromeContentBrowserClientExtensionsPart::RenderProcessWillLaunch(
 
   host->AddFilter(new ChromeExtensionMessageFilter(id, profile));
   host->AddFilter(new ExtensionMessageFilter(id, profile));
+  host->AddFilter(new IOThreadExtensionMessageFilter(id, profile));
   host->AddFilter(new GuestViewMessageFilter(id, profile));
   extension_web_request_api_helpers::SendExtensionWebRequestStatusToHost(host);
 }