Revert of Make the Sk GL context class an abstract base class

Revert of Make the Sk GL context class an abstract base class (patchset #4 id:60001 of https://codereview.chromium.org/630843002/)

Reason for revert:
nanobech failing on Android

Original issue's description:
> Make the Sk GL context class an abstract base class
> 
> Make the Sk GL context class, SkGLNativeContext, an abstract base class. Before,
> it depended on ifdefs to implement the platform dependent polymorphism.  Move
> the logic to subclasses of the various platform implementations.
> 
> This a step to enable Skia embedders to compile dm and bench_pictures. The
> concrete goal is to support running these test apps with Chromium command buffer.
> 
> With this change, Chromium can implement its own version of SkGLNativeContext
> that uses command buffer, and host the implementation in its own repository.
> 
> Implements the above by renaming the SkGLContextHelper to SkGLContext and
> removing the unneeded SkGLNativeContext. Also removes
> SkGLNativeContext::AutoRestoreContext functionality, it appeared to be unused:
> no use in Skia code, and no tests.
> 
> BUG=skia:2992
> 
> Committed: https://skia.googlesource.com/skia/+/a90ed4e83897b45d6331ee4c54e1edd4054de9a8

TBR=kkinnunen@nvidia.com
NOTREECHECKS=true
NOTRY=true
BUG=skia:2992
Committed: https://skia.googlesource.com/skia/+/10805961ce424868e8315e00f6dbeeaa62d466ac

[bsalomon, 2014-10-08 11:43:55]

Created Revert of Make the Sk GL context class an abstract base class

[commit-bot: I haz the power, 2014-10-08 11:44:44]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/639793002/1

[commit-bot: I haz the power, 2014-10-08 11:45:15]

Committed patchset #1 (id:1) as 10805961ce424868e8315e00f6dbeeaa62d466ac