Manually load CONDITION_VARIABLE methods on Windows, checking for failure (XP).

Manually load CONDITION_VARIABLE methods on Windows, checking for failure (XP).

Tested by running DM on XP.  Before this patch, it fails at startup (even just out/Debug/dm --help).  Now it asserts for other reasons later on in user code, which is just fine by me.

The net effect is that SkTaskGroups will always be synchronous on XP.  That's not ideal, but a step up from crashing.

CQ_EXTRA_TRYBOTS=client.skia:Test-Win7-ShuttleA-HD2000-x86-Release-Trybot,Test-Win7-ShuttleA-HD2000-x86_64-Release-Trybot

BUG=skia:

Committed: https://skia.googlesource.com/skia/+/db8d0e5bb018594d0ced3bfa68484115d8cf76b8

[mtklein, 2014-11-03 21:58:33]

The CQ bit was checked by mtklein@google.com

[commit-bot: I haz the power, 2014-11-03 21:59:14]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/700683002/20001

[commit-bot: I haz the power, 2014-11-03 21:59:15]

Note for Reviewers:
The CQ is waiting for an approval.
If you believe that the CL is not ready yet, or if you would like to L-G-T-M
with comments then please uncheck the CQ checkbox.

Waiting for LGTM from valid reviewer(s) till 2014-11-04 03:59 UTC

[mtklein, 2014-11-03 21:59:50]

The CQ bit was unchecked by mtklein@google.com

[mtklein, 2014-11-03 22:01:26]

mtklein@google.com changed reviewers:
+ bungeman@google.com

[reed1, 2014-11-03 22:03:40]

reed@google.com changed reviewers:
+ reed@google.com

[reed1, 2014-11-03 22:03:41]

lgtm

[mtklein, 2014-11-03 22:24:53]

The CQ bit was checked by mtklein@google.com

[commit-bot: I haz the power, 2014-11-03 22:25:17]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/700683002/40001

[commit-bot: I haz the power, 2014-11-03 22:25:20]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-11-03 22:25:20]

Transient error: Invalid delimiter in
"Test-Win7-ShuttleA-HD2000-x86-Release-Trybot,Test-Win7-ShuttleA-HD2000-x86_64-Release-Trybot":
Correct syntax is "tryserver:bot1,bot2;tryserver2:bot3,bot4;".

[mtklein, 2014-11-03 22:25:47]

The CQ bit was checked by mtklein@google.com

[commit-bot: I haz the power, 2014-11-03 22:25:49]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/700683002/40001

[commit-bot: I haz the power, 2014-11-04 01:25:57]

Committed patchset #3 (id:40001) as db8d0e5bb018594d0ced3bfa68484115d8cf76b8