Add postMessage APIs to the support lib

customtabs/src/android/support/customtabs/CustomTabsClient.java

Index: customtabs/src/android/support/customtabs/CustomTabsClient.java
diff --git a/customtabs/src/android/support/customtabs/CustomTabsClient.java b/customtabs/src/android/support/customtabs/CustomTabsClient.java
index f743c7dde92ee3f73648368dc239181506af09e7..3abde9b7cea92bd377be9825f8e2c7e9aec0d5fb 100644
--- a/customtabs/src/android/support/customtabs/CustomTabsClient.java
+++ b/customtabs/src/android/support/customtabs/CustomTabsClient.java
@@ -24,6 +24,8 @@ import android.content.pm.PackageManager;
 import android.content.pm.ResolveInfo;
 import android.net.Uri;
 import android.os.Bundle;
+import android.os.Handler;
+import android.os.Looper;
 import android.os.RemoteException;
 import android.support.annotation.Nullable;
 import android.text.TextUtils;
@@ -173,21 +175,57 @@ public class CustomTabsClient {
      * then later with a Custom Tab. The client can then send later service calls or intents to
      * through same session-intent-Custom Tab association.
      * @param callback The callback through which the client will receive updates about the created
-     *                 session. Can be null.
+     *                 session. Can be null. All the callbacks will be received on the UI thread.
      * @return The session object that was created as a result of the transaction. The client can
-     *         use this to relay {@link CustomTabsSession#mayLaunchUrl(Uri, Bundle, List)} calls.
+     *         use this to relay session specific calls.
      *         Null on error.
      */
     public CustomTabsSession newSession(final CustomTabsCallback callback) {

[Benoit L, 2016/11/08 16:27:06]

nit: Can be deferred to a subsequent CL, but we are now using the android
support library annotations in several places, so it probably makes sense to put
@NonNull and @Nullable annotations to params as we update the methods. Hopefully
this is useful to Android Studio users...

[Yusuf, 2016/11/08 18:59:10]

Acknowledged.

         ICustomTabsCallback.Stub wrapper = new ICustomTabsCallback.Stub() {
+            Handler mHandler = new Handler(Looper.getMainLooper());
+
             @Override
             public void onNavigationEvent(int navigationEvent, Bundle extras) {

[Benoit L, 2016/11/08 16:27:06]

Does it compile?
I would expect that the parameters need to be final (here and below).

[Yusuf, 2016/11/08 18:59:10]

Caught me! No, it doesn't.

-                if (callback != null) callback.onNavigationEvent(navigationEvent, extras);
+                if (callback = null) return;
+                mHandler.post(new Runnable() {
+                    @Override
+                    public void run() {
+                        callback.onNavigationEvent(navigationEvent, extras);
+                    }
+                });
+            }
+
+            @Override
+            public void onMessageChannelReady(Uri origin, Bundle extras) {
+                if (callback = null) return;
+                mHandler.post(new Runnable() {
+                    @Override
+                    public void run() {
+                        callback.onMessageChannelReady(origin, extras);
+                    }
+                });
+            }
+
+            @Override
+            public void onPostMessage(String message, Bundle extras) {
+                if (callback = null) return;
+                mHandler.post(new Runnable() {
+                    @Override
+                    public void run() {
+                        callback.onPostMessage(message, extras);
+                    }
+                });
             }
 
             @Override
             public void extraCallback(String callbackName, Bundle args) throws RemoteException {
-                if (callback != null) callback.extraCallback(callbackName, args);
+                if (callback = null) return;
+                mHandler.post(new Runnable() {
+                    @Override
+                    public void run() {
+                        callback.extraCallback(callbackName, args);
+                    }
+                });
             }
         };