DevTools: Extract CPU profile model out of CPUProfileView.

CPUFlameChartDataProvider is made to not depend on CPUProfileView.

Review URL: https://codereview.chromium.org/235453008

git-svn-id: svn://svn.chromium.org/blink/trunk@171445 bbb929c8-8fbe-4397-9dbb-9b2b20218538