DevTools: filter out annotations from skia command log and attach them to actual commands

- process command log in PaintProfilerSnapshot.commandLog()
- remove annotations as indenepdent log entris and attach them
    to actual commands they annotate;
- maintain original indices of commands in the log, use them when requesting snapshots;
- iterate over filetered log, not original timings, when displaying
    time chart.

Review URL: https://codereview.chromium.org/384633004

git-svn-id: svn://svn.chromium.org/blink/trunk@177835 bbb929c8-8fbe-4397-9dbb-9b2b20218538