[Custom tab]Fix a bug that clicking media notification opens blank tab

chrome/android/java/src/org/chromium/chrome/browser/media/MediaCaptureNotificationService.java

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 package org.chromium.chrome.browser.media;
 
 import android.app.Notification;
 import android.app.NotificationManager;
 import android.app.PendingIntent;
 import android.app.Service;
@@ skipping 141 matching lines @@
             notificationContentTextId = R.string.video_audio_call_notification_text_2;
             notificationIconId = R.drawable.webrtc_video;
         } else if (mediaType == MEDIATYPE_VIDEO_ONLY) {
             notificationContentTextId = R.string.video_call_notification_text_2;
             notificationIconId = R.drawable.webrtc_video;
         } else if (mediaType == MEDIATYPE_AUDIO_ONLY) {
             notificationContentTextId = R.string.audio_call_notification_text_2;
             notificationIconId = R.drawable.webrtc_audio;
         }
 
-        Intent tabIntent = Tab.createBringTabToFrontIntent(notificationId);
-        PendingIntent contentIntent = PendingIntent.getActivity(
-                mContext, notificationId, tabIntent, 0);
         String contentText = mContext.getResources().getString(notificationContentTextId) + ". "
                 + mContext.getResources().getString(
                         R.string.media_notification_link_text, url);
 
         NotificationCompat.Builder builder = new NotificationCompat.Builder(mContext)
                 .setAutoCancel(false)
                 .setOngoing(true)
-                .setContentIntent(contentIntent)
                 .setContentTitle(mContext.getString(R.string.app_name))
                 .setContentText(contentText)
                 .setSmallIcon(notificationIconId)
                 .setLocalOnly(true);
 
+        Intent tabIntent = Tab.createBringTabToFrontIntent(notificationId);
+        if (tabIntent != null) {
+            PendingIntent contentIntent = PendingIntent.getActivity(
+                    mContext, notificationId, tabIntent, 0);
+            builder.setContentIntent(contentIntent);
+        }
+
         Notification notification = new NotificationCompat.BigTextStyle(builder)
                 .bigText(contentText).build();
         mNotificationManager.notify(NOTIFICATION_NAMESPACE, notificationId, notification);
         mNotifications.put(notificationId, mediaType);
         updateSharedPreferencesEntry(notificationId, false);
     }
 
     /**
      * Update shared preferences entry with ids of the visible notifications.
      * @param notificationId Id of the notification.
@@ skipping 94 matching lines @@
     public static void clearMediaNotifications(Context context) {
         SharedPreferences sharedPreferences =
                 PreferenceManager.getDefaultSharedPreferences(context);
         Set<String> notificationIds =
                 sharedPreferences.getStringSet(WEBRTC_NOTIFICATION_IDS, null);
         if (notificationIds == null || notificationIds.isEmpty()) return;
 
         context.startService(new Intent(context, MediaCaptureNotificationService.class));
     }
 }