TimelinePanel: initial implementation of FlameChart in TimelinePanel.

It works but doesn't support:
a) Details pane info for the selected item,
b) jump to function. We have no jumpable items at the moment.
c) zoom in the main FlameChart pane. It can be zoomed only via Overview pane.

BUG=316167
R=pfeldman@chromium.org

Review URL: https://codereview.chromium.org/143793003

git-svn-id: svn://svn.chromium.org/blink/trunk@166820 bbb929c8-8fbe-4397-9dbb-9b2b20218538