Disable fetching of thumbnails when using snapshots.

- We don't keep the snapshots on the SysUI side so this is just a wasted
  call to load them (the rest of the metadata can still be prefetched
  though).

Test: Launch new tasks and ensure that we aren't fetching task snapshots
      without entering overview.

Change-Id: I1fe01a162f15e4f75b333e7e1bbe32d07e5d0b8d

packages/SystemUI/src/com/android/systemui/recents/RecentsImpl.java

@@ -130,6 +130,7 @@ public class RecentsImpl implements ActivityOptions.OnAnimationFinishedListener
                 launchOpts.numVisibleTaskThumbnails = 2;
                 launchOpts.onlyLoadForCache = true;
                 launchOpts.onlyLoadPausedActivities = true;
+                launchOpts.loadThumbnails = !ActivityManager.ENABLE_TASK_SNAPSHOTS;
                 loader.loadTasks(mContext, plan, launchOpts);
             }
         }