Add postMessage APIs to the support lib

customtabs/src/android/support/customtabs/CustomTabsSession.java

Index: customtabs/src/android/support/customtabs/CustomTabsSession.java
diff --git a/customtabs/src/android/support/customtabs/CustomTabsSession.java b/customtabs/src/android/support/customtabs/CustomTabsSession.java
index 290150db1837a46d9a91c9aae52396cbafaf3cf7..8157733298b700d7a0cb65e82d6884b2159460bb 100644
--- a/customtabs/src/android/support/customtabs/CustomTabsSession.java
+++ b/customtabs/src/android/support/customtabs/CustomTabsSession.java
@@ -24,6 +24,7 @@ import android.os.Bundle;
 import android.os.IBinder;
 import android.os.RemoteException;
 import android.support.annotation.NonNull;
+import android.support.customtabs.CustomTabsService.Result;
 import android.support.customtabs.CustomTabsSessionToken.DummyCallback;
 import android.widget.RemoteViews;
 
@@ -150,6 +151,23 @@ public final class CustomTabsSession {
         }
     }
 
+    public boolean validatePostMessageOrigin() {
+        try {
+            return mService.validatePostMessageOrigin(mCallback);
+        } catch (RemoteException e) {
+            return false;
+        }
+    }
+
+    @Result
+    public synchronized int postMessage(String message, Bundle extras) {
+        try {
+            return mService.postMessage(mCallback, message, extras);
+        } catch (RemoteException e) {
+            return CustomTabsService.RESULT_FAILURE_REMOTE_ERROR;
+        }
+    }
+
     /* package */ IBinder getBinder() {
         return mCallback.asBinder();
     }