Implement CRC2D.scrollPathIntoView() on Canvas

The method's behavior is very similar to element.scrollIntoView().
This is just a another version about path on canvas.
('path' means both current default path and path object)
This is especially useful on devices with small screens,
where the whole canvas might not be visible at once.

Intent to Implement:
  https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/KLFSBeP42VQ

The spec reference is:
  http://www.w3.org/TR/2dcontext/#dom-context-2d-scrollpathintoview
  http://www.whatwg.org/specs/web-apps/current-work/#dom-context-2d-scrollpathintoview

BUG=351696

Review URL: https://codereview.chromium.org/196243007

git-svn-id: svn://svn.chromium.org/blink/trunk@170524 bbb929c8-8fbe-4397-9dbb-9b2b20218538