Merge "Fix issue #7214462: Some recent thumbnails are black." into jb-mr1-dev

Author: Dianne Hackborn

services/java/com/android/server/am/ActivityStack.java

@@ -4329,6 +4329,9 @@ public ActivityManager.TaskThumbnails getTaskThumbnailsLocked(TaskRecord tr) {
         if (resumed != null && resumed.thumbHolder == tr) {
             info.mainThumbnail = resumed.stack.screenshotActivities(resumed);
         }
+        if (info.mainThumbnail == null) {
+            info.mainThumbnail = tr.lastThumbnail;
+        }
         return info;
     }
 
@@ -4343,7 +4346,7 @@ public Bitmap getTaskTopThumbnailLocked(TaskRecord tr) {
         // thumbnail to return.
         TaskAccessInfo info = getTaskAccessInfoLocked(tr.taskId, true);
         if (info.numSubThumbbails <= 0) {
-            return info.mainThumbnail;
+            return info.mainThumbnail != null ? info.mainThumbnail : tr.lastThumbnail;
         } else {
             return info.subtasks.get(info.numSubThumbbails-1).holder.lastThumbnail;
         }