Move CanvasResourceProvider ownership up to CanvasResourceHost

This change pushes HTMLCanvasElement's CanvasResourceProvider
up the class hierachy so that it can be shared with
OffscreenCanvas. The next step is to remove
Canvas2DLayerBridge's resource provider to use this shared one
instead.

BUG=788439
TBR=zmo@chromium.org

Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win_optional_gpu_tests_rel;master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
Change-Id: Ib85237d0ee98205c5da8848cbd861ce6d5d9d4d2
Reviewed-on: https://chromium-review.googlesource.com/1075729
Commit-Queue: Justin Novosad <junov@chromium.org>
Reviewed-by: Fernando Serboncini <fserb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#562433}
8 files changed