Remove GraphicsContextCG.

Remove GraphicsContextCG.

We haven't supported Core Graphics in some time.
Only one of these functions is implemented at all, and it  is unused.

BUG=381789
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=175724

[f(malita), 2014-06-06 18:43:52]

lgtm

[jbroman, 2014-06-06 18:44:42]

The CQ bit was checked by jbroman@chromium.org

[commit-bot: I haz the power, 2014-06-06 18:45:17]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/jbroman@chromium.org/315403007/20001

[commit-bot: I haz the power, 2014-06-06 19:39:09]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  win_gpu_triggered_tests on tryserver.chromium.gpu
(http://build.chromium.org/p/tryserver.chromium.gpu/builders/win_gpu_triggered...)

[commit-bot: I haz the power, 2014-06-06 19:39:17]

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

[commit-bot: I haz the power, 2014-06-06 19:39:18]

Try jobs failed on following builders:
  win_gpu_triggered_tests on tryserver.chromium.gpu
(http://build.chromium.org/p/tryserver.chromium.gpu/builders/win_gpu_triggered...)

[jbroman, 2014-06-07 01:59:15]

The CQ bit was checked by jbroman@chromium.org

[commit-bot: I haz the power, 2014-06-07 02:00:09]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/jbroman@chromium.org/315403007/20001

[commit-bot: I haz the power, 2014-06-07 03:30:46]

Change committed as 175724