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

extensions/shell/browser/shell_content_browser_client.cc

Index: extensions/shell/browser/shell_content_browser_client.cc
diff --git a/extensions/shell/browser/shell_content_browser_client.cc b/extensions/shell/browser/shell_content_browser_client.cc
index 8efc910710a5ce55cfba7900aee4f1b1828d71a9..905a3438ff89265e5c77973c92c20df6d284dcb4 100644
--- a/extensions/shell/browser/shell_content_browser_client.cc
+++ b/extensions/shell/browser/shell_content_browser_client.cc
@@ -17,6 +17,7 @@
 #include "extensions/browser/extension_registry.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/process_map.h"
 #include "extensions/common/constants.h"
 #include "extensions/common/extension.h"
@@ -82,6 +83,8 @@ void ShellContentBrowserClient::RenderProcessWillLaunch(
   host->AddFilter(
       new ExtensionMessageFilter(render_process_id, browser_context));
   host->AddFilter(
+      new IOThreadExtensionMessageFilter(render_process_id, browser_context));
+  host->AddFilter(
       new GuestViewMessageFilter(render_process_id, browser_context));
   // PluginInfoMessageFilter is not required because app_shell does not have
   // the concept of disabled plugins.