1286b571ff
If an input ANR is caused by the lock of window manager
or activity manager is held for a long time, we usually
get an unhelpful stack traces because the ANR reporting
is also blocked by the locks.
The pre-dump checks if the locks cannot be acquired within
a timeout, then dump the stack trace at the beginning of
notifying ANR.
Bug: 144987910
Test: 1. Launch a simple app.
2. Set break-points inside the lock of window manager
and activity manager.
3. Press back key and wait 5s.
4. Check the path /data/anr/ in device. There should
be a filename ends with "_pre".
Change-Id: I9831a31e17661d822572c73e64fe9980fe018b22