cc: Fix and simplify DelayBasedTimeSource

- This converts some floating point math to integer math
to avoid rounding errors.

- Assigns last_tick_time_ to be the time it was *supposed*
to tick and no longer uses it as a synonym for "now".

- Adds trace events to help debug when the interval or
phase changes.

BUG=256650

Review URL: https://chromiumcodereview.appspot.com/18589002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@210101 0039d316-1c4b-4281-b951-d872f2087c98
3 files changed