Fix display list canvas fallback to GPU accelerated mode

Fix display list canvas fallback to GPU accelerated mode

Right now when the display list canvas fallback is triggered,
and the fallback canvas is GPU-acclerated, we fail to notify
the GraphicsContext that it has become
accelerated.  This causes HTMLCanvasElement::paint to use
the CPU rendering code path. This change fix the problem by
notifying the GraphicsContext of whether GPU acceleration
is use by the fallback canvas.

BUG=426169
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=184379

[Justin Novosad, 2014-10-22 20:20:34]

junov@chromium.org changed reviewers:
+ senorblanco@chromium.org
- senorblanco@google.com

[Justin Novosad, 2014-10-24 17:31:42]

review ping.

[Stephen White, 2014-10-24 17:44:15]

Tests would be nice, but LGTM since it's small.

[Justin Novosad, 2014-10-24 17:54:05]

The CQ bit was checked by junov@chromium.org

[commit-bot: I haz the power, 2014-10-24 17:54:54]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/669993004/1

[Justin Novosad, 2014-10-24 18:08:27]

FYI: We'll have all the testing we need once we flip the switch on the telemetry
tests

[commit-bot: I haz the power, 2014-10-24 19:28:28]

Committed patchset #1 (id:1) as 184379