Detect bad behavior earlier in Choreographer.

Detect wonky vsync timestamps (should they occur) and
warn loudly about them.

Warn when too many frames are skipped.  The threshold is pretty
conservative right now (only warn if at least 30 frames are skipped)
but it can be adjusted using system property.  Even skipping just a
couple of frames is enough to generate noticeable jank.
The threshold is currently intended to help track down bigger problems
such when an app does too much work on the UI thread.

Bug: 6574842
Change-Id: I4aac7e5e17d1fb51adb0510e318a72a28b3775ed