Fix an early return and the error status in glLoseContextCHROMIUM impl

Fix an early return and the error status in glLoseContextCHROMIUM impl

The implementation of glLoseContextCHROMIUM did not return early
in gl error conditions of invalid enums passed as arguments. Add
the early returns and tests for the invalid enums.

Upon successful glLoseContextCHROMIUM, the subsequent calls
such as glGetError would also fail, because the implementation
would set the decoder error variable as well as return the error
value. Fix this by just setting the decoder error variable. Add
a test for this (LoseContextCHROMIUMValidArgs)

BUG=373159
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=272507

[Kimmo Kinnunen, 2014-05-21 07:29:45]

the lose context part of the missing return values bug.

[piman, 2014-05-21 20:57:33]

lgtm

[vmiura, 2014-05-22 05:02:36]

lgtm

[Kimmo Kinnunen, 2014-05-23 08:22:50]

The CQ bit was checked by kkinnunen@nvidia.com

[commit-bot: I haz the power, 2014-05-23 08:23:47]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/kkinnunen@nvidia.com/298753004/1

[commit-bot: I haz the power, 2014-05-23 13:05:05]

Change committed as 272507