DevTools: move CPUFlameChart color generator into the CPUFlameChartDataProvider

CPUFlameChartDataProvider should not depend on CPUProfileView

Review URL: https://codereview.chromium.org/235943014

git-svn-id: svn://svn.chromium.org/blink/trunk@171570 bbb929c8-8fbe-4397-9dbb-9b2b20218538