Revert 244383 "Use ContextProvider subclass to provide WGC3D poi..."

Likely cause of WebGL conformance test crashes on Android GPU bot.

BUG=333761,181120

> Use ContextProvider subclass to provide WGC3D pointers
> 
> Some cc::ContextProvider instances will also need to provide WebGraphicsContext3D*
> interfaces to the underlying GL context, but not all. This adds a subclass of ContextProvider
> in content:: to use for these users. The compositor itself doesn't need the WGC3D
> accessor so it just uses the base class.
> 
> BUG=181120
> 
> Review URL: https://codereview.chromium.org/126093010

TBR=jamesr@chromium.org

Review URL: https://codereview.chromium.org/136273002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@244470 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 244470