Improve the thread flip.

- In addition to the threads that are suspended in FullSuspendCheck(),
  prioritize the resume of threads that are blocking for the thread
  flip at the JNI critical section entry and threads are about to
  transition to runnable (eg. blocking at the SOA entry from JNI).
- Shorten the length of the thread flip critical
  section (ThreadFlipBegin/End).
- Add some systrace scopes.

Bug: 29517059
Bug: 12687968
Test: test-art-host, Ritz EAAC, N9 libartd boot.
Change-Id: Idecec9936ae432c23d5f83321ba13339852018df