Add canvas line segment tests

Add canvas line segment tests
https://bugs.webkit.org/show_bug.cgi?id=150073
<rdar://problem/23082138>

Reviewed by Dean Jackson.

* Animometer/runner/resources/tests.js: Add new line segment tests, with different
line caps.
* Animometer/tests/simple/resources/simple-canvas-paths.js:
(CanvasLineSegment): Add new line segment paint object.
(CanvasLineSegmentStage): Create a new stage that sets the lineCap.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@190918 268f45cc-cd09-0410-ab3c-d52691b4dbfc