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 c996cc43b24d89cec9bcb982ecae56d480163e1e..9bf982481b6c119b2dc85fa8e8dc7d18c84b2174 100644
--- a/android_webview/lib/main/aw_main_delegate.cc
+++ b/android_webview/lib/main/aw_main_delegate.cc
@@ -10,6 +10,7 @@
 #include "android_webview/lib/aw_browser_dependency_factory_impl.h"
 #include "android_webview/native/aw_assets.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"
@@ -172,6 +173,10 @@ AwWebPreferencesPopulater* AwMainDelegate::CreateWebPreferencesPopulater() {
   return new AwWebPreferencesPopulaterImpl();
 }
 
+AwMessagePortService* AwMainDelegate::CreateAwMessagePortService() {
+  return new AwMessagePortServiceImpl();
+}
+
 #if defined(VIDEO_HOLE)
 content::ExternalVideoSurfaceContainer*
 AwMainDelegate::CreateExternalVideoSurfaceContainer(