Add a service to handle postMessage callbacks to client

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

 /*
  * Copyright (C) 2015 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
@@ skipping 18 matching lines @@
 import android.widget.RemoteViews;
 
 import java.util.List;
 
 /**
  * A class to be used for Custom Tabs related communication. Clients that want to launch Custom Tabs
  * can use this class exclusively to handle all related communication.
  */
 public final class CustomTabsSession {
     private static final String TAG = "CustomTabsSession";
+    private final Object mLock = new Object();
     private final ICustomTabsService mService;
     private final ICustomTabsCallback mCallback;
     private final ComponentName mComponentName;
 
     /**
      * Provides browsers a way to generate a dummy {@link CustomTabsSession} for testing
      * purposes.
      *
      * @param componentName The component the session should be created for.
      * @return A dummy session with no functionality.
@@ skipping 95 matching lines @@
 
         Bundle metaBundle = new Bundle();
         metaBundle.putBundle(CustomTabsIntent.EXTRA_ACTION_BUTTON_BUNDLE, bundle);
         try {
             return mService.updateVisuals(mCallback, metaBundle);
         } catch (RemoteException e) {
             return false;
         }
     }
 
-    public boolean validatePostMessageOrigin() {
+    /**
+     * Sends a request to create a two way postMessage channel between the client and the browser.
+     *
+     * @param postMessageOrigin      A origin that the client is requesting to be identified as
+     *                               during the postMessage communication.
+     * @return Whether the implementation accepted the request. Note that returning true
+     *         here doesn't mean an origin has already been assigned as the validation is
+     *         asynchronous.
+     */
+    public boolean requestPostMessageChannel(Uri postMessageOrigin) {
         try {
-            return mService.validatePostMessageOrigin(mCallback);
+            return mService.requestPostMessageChannel(
+                    mCallback, postMessageOrigin);
         } catch (RemoteException e) {
             return false;
         }
     }
 
+    /**
+     * Sends a postMessage request using the origin communicated via
+     * {@link CustomTabsService#requestPostMessageChannel(
+     * CustomTabsSessionToken, Uri)}. Fails when called before
+     * {@link PostMessageServiceConnection#notifyMessageChannelReady(Bundle)} is received on
+     * the client side.
+     *
+     * @param message The message that is being sent.
+     * @param extras Reserved for future use.
+     * @return An integer constant about the postMessage request result.

[Benoit L, 2017/01/25 21:25:03]

nit: Perhaps specify where are these constants? (The Result "enum")

[Yusuf, 2017/01/25 22:02:00]

The most viable way to refer to the enum was to refer to one of the constants.

+     */
     @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;
+    public int postMessage(String message, Bundle extras) {
+        synchronized (mLock) {
+            try {
+                return mService.postMessage(mCallback, message, extras);
+            } catch (RemoteException e) {
+                return CustomTabsService.RESULT_FAILURE_REMOTE_ERROR;
+            }
         }
     }
 
     /* package */ IBinder getBinder() {
         return mCallback.asBinder();
     }
 
     /* package */ ComponentName getComponentName() {
         return mComponentName;
     }
 }