FlameChart: extract CPUProfiler related code into FlameChartDataProvider

We are going to support FlameChart in Timeline.
So we need to make it independent from the underlaying data.

It is the first patch from N.
In the next patches I'll
1) eliminate FlameChart.Entry class,
2) extract DataProvider interface
3) move the FlameChart code from ProfilesPanel to WebInspector.
4) implement DataProvider for Timeline

BUG=316167
R=yurys@chromium.org

Review URL: https://codereview.chromium.org/64093002

git-svn-id: svn://svn.chromium.org/blink/trunk@161530 bbb929c8-8fbe-4397-9dbb-9b2b20218538