Using "static_assert" in lieu of "COMPILE_ASSERT" in extensions module

Using "static_assert" in lieu of "COMPILE_ASSERT"  in extensions module

All our toolchains support c++'s static_assert now- COMPILE_ASSERT can be removed now.

BUG=442514
Committed: https://crrev.com/200c95464e96ae99f3855c47dd8a7ca80fed620c
Cr-Commit-Position: refs/heads/master@{#313230}

[anujsharma, 2015-01-20 13:52:42]

anujk.sharma@samsung.com changed reviewers:
+ rockot@chromium.org

[anujsharma, 2015-01-20 13:52:43]

PTAL

[anujsharma, 2015-01-26 10:32:25]

anujk.sharma@samsung.com changed reviewers:
+ kalman@chromium.org

[anujsharma, 2015-01-26 10:33:41]

@Kalman,
Could you please help me in land this CL.
PTAL

Thanks!!

[not at google - send to devlin, 2015-01-26 16:14:21]

lgtm

[anujsharma, 2015-01-27 03:23:48]

On 2015/01/26 16:14:21, kalman wrote:
> lgtm

Thanks kalman for lgtm.

[anujsharma, 2015-01-27 03:23:52]

The CQ bit was checked by anujk.sharma@samsung.com

[commit-bot: I haz the power, 2015-01-27 03:24:32]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/859993002/1

[commit-bot: I haz the power, 2015-01-27 04:56:46]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-01-27 04:57:44]

Patchset 1 (id:??) landed as
https://crrev.com/200c95464e96ae99f3855c47dd8a7ca80fed620c
Cr-Commit-Position: refs/heads/master@{#313230}