simpleperf: fix inferno and test content of report.html.

simpleperf: fix inferno and test content of report.html.

Inferno uses sample count to decide the width of each method,
but this is not accurate. Fix it by using event count instead.

Besides that, refactor inferno.py a little, get record cmd
and device info from perf.data, and test content of report.html
generated by inferno.

Also fix a flakey test TestExamplePureJava.test_app_profiler_with_ctrl_c.

Bug: http://b/64035530
Test: run test.py.
Change-Id: Ia57fcbd28b4242b4251b063bd38a58da7b93eba0