Don't hold lock when dumping activities of app side

Although TransferPipe has a 5s timeout, there may have
several activities take long time do dump that may lead
to system no response.

Fix: 135770637
Test: Launch an activity which overrides Activity#dump
      and sleeps 5s in the dump method. Enter command:
      "adb shell dumpsys activity all", then check the
      interaction with system UI is still responsive.

Change-Id: Id81463eee0178065a0fb982a6e599bee5f15dd81