Enable Path2D object and some path APIs by default.

Enable following APIs:
  - Path2D Object Constructor & Inteface
  - void fill(Path2D, optional CanvasFillRule);
  - void stroke(Path2D);
  - void clip(Path2D, optional CanvasFillRule);
  - boolean isPointInPath(Path2D, x, y, optional CanvasFillRule);
  - boolean isPointInStroke(Path2D, x, y);

Intent to Ship:
  https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/mhjb3Em8H0A

BUG=159839,330506

Review URL: https://codereview.chromium.org/227583006

git-svn-id: svn://svn.chromium.org/blink/trunk@171302 bbb929c8-8fbe-4397-9dbb-9b2b20218538