Take extensions out of Profile into a profile-keyed service, ExtensionSystem.

chrome/browser/extensions/extension_message_handler.cc

Index: chrome/browser/extensions/extension_message_handler.cc
diff --git a/chrome/browser/extensions/extension_message_handler.cc b/chrome/browser/extensions/extension_message_handler.cc
index 0ad400511aab1449254cfa634735e9471647acd6..9e2e838f22c37227c3b8144b1f053363382633d6 100644
--- a/chrome/browser/extensions/extension_message_handler.cc
+++ b/chrome/browser/extensions/extension_message_handler.cc
@@ -5,6 +5,8 @@
 #include "chrome/browser/extensions/extension_message_handler.h"
 
 #include "chrome/browser/extensions/extension_message_service.h"
+#include "chrome/browser/extensions/extension_system.h"
+#include "chrome/browser/extensions/extension_system_factory.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/common/extensions/extension_messages.h"
 #include "content/browser/renderer_host/render_view_host.h"
@@ -38,8 +40,9 @@ void ExtensionMessageHandler::OnPostMessage(int port_id,
                                             const std::string& message) {
   Profile* profile = Profile::FromBrowserContext(
       render_view_host()->process()->GetBrowserContext());
-  if (profile->GetExtensionMessageService()) {
-    profile->GetExtensionMessageService()->PostMessageFromRenderer(
-        port_id, message);
+  ExtensionMessageService* message_service =
+      ExtensionSystemFactory::GetForProfile(profile)->message_service();
+  if (message_service) {
+    message_service->PostMessageFromRenderer(port_id, message);
   }
 }