[Android MR] Fix a crasher when registering/unregistering callback

The crasher happens when the session is connected/disconnected. The code
registers/unregisters RemoteMediaClient callback upon
connecting/disconnecting. However it should check the availability of
RemoteMediaClient of the current session.

Bug: 711860
Change-Id: Ie4b29f507a0044ac8649b52b37f1541e4dc9b4ee
Reviewed-on: https://chromium-review.googlesource.com/c/1350211
Commit-Queue: Zhiqiang Zhang <zqzhang@chromium.org>
Reviewed-by: Thomas Guilbert <tguilbert@chromium.org>
Cr-Commit-Position: refs/heads/master@{#611030}

chrome/android/java/src/org/chromium/chrome/browser/media/router/caf/BaseSessionController.java

@@ -128,14 +128,20 @@ public class BaseSessionController {
     /** Attaches the controller to the current {@link CastSession}. */
     public void attachToCastSession(CastSession session) {
         mCastSession = session;
-        getRemoteMediaClient().registerCallback(mRemoteMediaClientCallback);
+        RemoteMediaClient uncheckedRemoteMediaClient = mCastSession.getRemoteMediaClient();
+        if (uncheckedRemoteMediaClient != null) {
+            uncheckedRemoteMediaClient.registerCallback(mRemoteMediaClientCallback);
+        }
     }
 
     /** Detaches the controller from any {@link CastSession}. */
     public void detachFromCastSession() {
         if (mCastSession == null) return;
 
-        getRemoteMediaClient().unregisterCallback(mRemoteMediaClientCallback);
+        RemoteMediaClient uncheckedRemoteMediaClient = mCastSession.getRemoteMediaClient();
+        if (uncheckedRemoteMediaClient != null) {
+            uncheckedRemoteMediaClient.unregisterCallback(mRemoteMediaClientCallback);
+        }
         mCastSession = null;
     }
 

chrome/android/junit/src/org/chromium/chrome/browser/media/router/caf/BaseSessionControllerTest.java

@@ -14,6 +14,7 @@ import static org.mockito.Mockito.anyInt;
 import static org.mockito.Mockito.anyString;
 import static org.mockito.Mockito.doReturn;
 import static org.mockito.Mockito.eq;
+import static org.mockito.Mockito.inOrder;
 import static org.mockito.Mockito.never;
 import static org.mockito.Mockito.verify;
 
@@ -32,6 +33,7 @@ import org.junit.Before;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.mockito.ArgumentCaptor;
+import org.mockito.InOrder;
 import org.mockito.Mock;
 import org.mockito.MockitoAnnotations;
 import org.robolectric.RuntimeEnvironment;
@@ -167,13 +169,27 @@ public class BaseSessionControllerTest {
 
     @Test
     public void testSessionAttachment() {
+        InOrder inOrder = inOrder(mRemoteMediaClient);
+
+        mController.attachToCastSession(mCastSession);
+        assertSame(mController.getSession(), mCastSession);
+        inOrder.verify(mRemoteMediaClient).registerCallback(any(RemoteMediaClient.Callback.class));
+
+        mController.detachFromCastSession();
+        assertNull(mController.getSession());
+        inOrder.verify(mRemoteMediaClient)
+                .unregisterCallback(any(RemoteMediaClient.Callback.class));
+
+        // Attaching/detaching while the session is disconnected.
+        doReturn(false).when(mCastSession).isConnected();
         mController.attachToCastSession(mCastSession);
         assertSame(mController.getSession(), mCastSession);
-        verify(mRemoteMediaClient).registerCallback(any(RemoteMediaClient.Callback.class));
+        inOrder.verify(mRemoteMediaClient).registerCallback(any(RemoteMediaClient.Callback.class));
 
         mController.detachFromCastSession();
         assertNull(mController.getSession());
-        verify(mRemoteMediaClient).unregisterCallback(any(RemoteMediaClient.Callback.class));
+        inOrder.verify(mRemoteMediaClient)
+                .unregisterCallback(any(RemoteMediaClient.Callback.class));
     }
 
     @Test