Fixing issue with recents not being hidden for translucent apps.

- When tapping home, we can't depend on the stack state to determine
  whether or not hide recents since there can be translucent windows
  above it.  In this case, we just dismiss recents directly since the
  receiver will only be registered while recents is visible.

Bug: 20110140

Change-Id: I6b796cc4cbd790aac9a0857549e34117adb808d8