Enable posting a message from JS to Android webview.

android_webview/lib/main/aw_main_delegate.cc

Index: android_webview/lib/main/aw_main_delegate.cc
diff --git a/android_webview/lib/main/aw_main_delegate.cc b/android_webview/lib/main/aw_main_delegate.cc
index f51215798452faf3b9dbef2336ca0e82c780b3a0..2072ea9c76ad2f77640edd0eab02ccdd4df714f4 100644
--- a/android_webview/lib/main/aw_main_delegate.cc
+++ b/android_webview/lib/main/aw_main_delegate.cc
@@ -9,6 +9,7 @@
 #include "android_webview/browser/scoped_allow_wait_for_legacy_web_view_api.h"
 #include "android_webview/lib/aw_browser_dependency_factory_impl.h"
 #include "android_webview/native/aw_media_url_interceptor.h"
+#include "android_webview/native/aw_message_port_service_impl.h"
 #include "android_webview/native/aw_quota_manager_bridge_impl.h"
 #include "android_webview/native/aw_web_contents_view_delegate.h"
 #include "android_webview/native/aw_web_preferences_populater_impl.h"
@@ -156,6 +157,10 @@ AwWebPreferencesPopulater* AwMainDelegate::CreateWebPreferencesPopulater() {
   return new AwWebPreferencesPopulaterImpl();
 }
 
+AwMessagePortService* AwMainDelegate::CreateAwMessagePortService() {
+  return new AwMessagePortServiceImpl();
+}
+
 #if defined(VIDEO_HOLE)
 content::ExternalVideoSurfaceContainer*
 AwMainDelegate::CreateExternalVideoSurfaceContainer(