Convert LayoutTests/fast/canvas/2d tests to testharness.

This patch uses testharness.js asserts to test
2d.text.draw.fill.maxWidth.gradient.html,
2d.text.draw.fill.maxWidth.negative-expected.html.
Remove the expectation files as they are not needed any more.

BUG=639732

Review-Url: https://codereview.chromium.org/2279763002
Cr-Commit-Position: refs/heads/master@{#414912}
4 files changed