DevTools: Allow PieChart of arbitrary size

Implement pie chart with SVG.
Increase pie chart size in heap snapshot view.
Drive-by: slices are now antialiased.

Review URL: https://codereview.chromium.org/194983002

git-svn-id: svn://svn.chromium.org/blink/trunk@168936 bbb929c8-8fbe-4397-9dbb-9b2b20218538