Refactor Canvas2DLayerBridge tests to use CanvasResourceProviderHost

This change prepares unit tests for having a new dependency on
CanvasResourceProviderHost, which will soon be the owner
of the CanvasResourceProvider instance used by 2D canvas.

Drive-by refactor: some tests that were formerly implemented in
fixture methods (for no good reason) were moved out.

BUG=788439

Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
Change-Id: I68331760a9ecb47efc6d91b185dd4ddc7a38dee8
Reviewed-on: https://chromium-review.googlesource.com/1077068
Reviewed-by: Fernando Serboncini <fserb@chromium.org>
Commit-Queue: Justin Novosad <junov@chromium.org>
Cr-Commit-Position: refs/heads/master@{#562600}
3 files changed