cc: Fix crash while running blink layout tests with GPU rasterization

cc: Fix crash with blink layout tests and GPU rasterization

We were missing the single-threaded task graph runner, which was
required for blink's layout tests that checked for pixels.

BUG=468928
Committed: https://crrev.com/ae0c69314c5c0025e8e6144f3a7fe64384087c77
Cr-Commit-Position: refs/heads/master@{#322192}

[hendrikw, 2015-03-24 22:55:25]

hendrikw@chromium.org changed reviewers:
+ enne@chromium.org

[hendrikw, 2015-03-24 22:55:34]

PTAL, thanks

[enne (OOO), 2015-03-24 23:08:55]

Do you think it makes sense to add this to the resource pixel tests? Or to test
this somehow?

[hendrikw, 2015-03-24 23:13:21]

On 2015/03/24 23:08:55, enne wrote:
> Do you think it makes sense to add this to the resource pixel tests? Or to
test
> this somehow?

Yeah, probably, I'll look into it.

[hendrikw, 2015-03-25 15:12:32]

On 2015/03/24 23:13:21, hendrikw wrote:
> On 2015/03/24 23:08:55, enne wrote:
> > Do you think it makes sense to add this to the resource pixel tests? Or to
> test
> > this somehow?
> 
> Yeah, probably, I'll look into it.

Test added, ptal, thanks

[enne (OOO), 2015-03-25 17:10:22]

The CQ bit was checked by enne@chromium.org

[enne (OOO), 2015-03-25 17:10:22]

lgtm

https://codereview.chromium.org/1036693002/diff/40001/cc/trees/layer_tree_hos...
File cc/trees/layer_tree_host_pixeltest_synchronous.cc (right):

https://codereview.chromium.org/1036693002/diff/40001/cc/trees/layer_tree_hos...
cc/trees/layer_tree_host_pixeltest_synchronous.cc:47: class
LayerTreeHostSynchronousGPUPixelTest : public LayerTreePixelTest {
Ooh, perfect.  Thanks!

[commit-bot: I haz the power, 2015-03-25 17:10:59]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1036693002/40001

[commit-bot: I haz the power, 2015-03-25 18:16:25]

Committed patchset #3 (id:40001)

[commit-bot: I haz the power, 2015-03-25 18:19:53]

Patchset 3 (id:??) landed as
https://crrev.com/ae0c69314c5c0025e8e6144f3a7fe64384087c77
Cr-Commit-Position: refs/heads/master@{#322192}