Log time of first paint and first paint after onload event

Add logging of paint times on browsers that support it:
- on Chrome, use chrome.loadTimes() to get time of first paint
  and time of first paint after the onload event
- on IE9+, use performance.timing.msFirstPaint to get time of
  first paint

First paint is a good approximation of when the user sees the page
content appearing. First paint after load is probably not that
useful, but might help detect problems with slow onload callbacks.

Bug: 65111
Change-Id: I13d860d6693776abd69e8d2f5636a48e8f194e69
Merge "Log time of first paint and first paint after onload event"