simpleperf: show event count in milliseconds in html interface.

1. Support showing event count in milliseconds in Chart tab and Sample tab.
2. Group meta info in Chart tab and Function tab in table chart.
3. Change app_profiler.py to use task-clock event by default, so we can
   show event count in milliseconds in html interface.

Bug: http://b/66914187
Test: Run report_html.py with demo apps.
Test: Run test.py.
Change-Id: Ieaff2d9d4e960429e9731a80117b57869af80338
4 files changed