DevTools: extract JS frames iterator out of CPUFlameChartDataProvider

... and move it to CPUProfileDataModel

BUG=363976
R=loislo@chromium.org

Review URL: https://codereview.chromium.org/244753002

git-svn-id: svn://svn.chromium.org/blink/trunk@172015 bbb929c8-8fbe-4397-9dbb-9b2b20218538