Fix a defect on a test runner for ppapi tests

ThreadedTestRunner::Run contained a PP_DCHECK with a side effect. Some tests failed because of it.
This CL fixes the problem.

BUG=None

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=213386

[dmichael (off chromium), 2013-07-22 16:15:32]

Oops, thanks! lgtm

[commit-bot: I haz the power, 2013-07-23 01:02:59]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/yhirano@chromium.org/19790011/1

[commit-bot: I haz the power, 2013-07-23 01:45:51]

Sorry for I got bad news for ya.
Compile failed with a clobber build on linux_aura.
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=linux_aura...
Your code is likely broken or HEAD is junk. Please ensure your
code is not broken then alert the build sheriffs.
Look at the try server FAQ for more details.

[commit-bot: I haz the power, 2013-07-23 01:45:58]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/yhirano@chromium.org/19790011/20001

[commit-bot: I haz the power, 2013-07-23 03:08:20]

Retried try job too often on linux_rel for step(s) sync_integration_tests
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=linux_rel&...

[commit-bot: I haz the power, 2013-07-23 03:48:36]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/yhirano@chromium.org/19790011/20001

[commit-bot: I haz the power, 2013-07-23 04:27:30]

Retried try job too often on linux_rel for step(s) sync_integration_tests
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=linux_rel&...

[commit-bot: I haz the power, 2013-07-24 03:33:12]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/yhirano@chromium.org/19790011/20001

[commit-bot: I haz the power, 2013-07-24 10:15:07]

Change committed as 213386