Revert of Revert of Extract most of the mutable state of SkShader into a separate Context object.

Revert of Revert of Extract most of the mutable state of SkShader into a separate Context object. (https://codereview.chromium.org/249643002/)

Reason for revert:
Chromium side change landed along side DEPS roll that includes r14323.

Original issue's description:
> Revert of Extract most of the mutable state of SkShader into a separate Context object. (https://codereview.chromium.org/207683004/)
> 
> Reason for revert:
> This is blocking the DEPS roll into Chromium. Failures can be seen here:
> 
> http://build.chromium.org/p/tryserver.chromium/builders/android_dbg/builds/174333
> 
> Original issue's description:
> > Extract most of the mutable state of SkShader into a separate Context object.
> > 
> > SkShader currently stores some state during draw calls via setContext(...).
> > Move that mutable state into a separate SkShader::Context class that is
> > constructed on demand for the duration of the draw.
> > 
> > Calls to setContext() are replaced with createContext() which returns a context
> > corresponding to the shader object or NULL if the parameters to createContext
> > are invalid.
> > 
> > TEST=out/Debug/dm
> > BUG=skia:1976
> > 
> > Committed: http://code.google.com/p/skia/source/detail?r=14216
> > 
> > Committed: http://code.google.com/p/skia/source/detail?r=14323
> 
> TBR=scroggo@google.com,skyostil@chromium.org,tomhudson@chromium.org,senorblanco@chromium.org,reed@google.com,bungeman@google.com,dominikg@chromium.org
> NOTREECHECKS=true
> NOTRY=true
> BUG=skia:1976
> 
> Committed: http://code.google.com/p/skia/source/detail?r=14326

TBR=scroggo@google.com,skyostil@chromium.org,tomhudson@chromium.org,senorblanco@chromium.org,reed@google.com,bungeman@google.com,dominikg@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=skia:1976
Committed: http://code.google.com/p/skia/source/detail?r=14328

[bsalomon, 2014-04-23 19:09:16]

Created Revert of Revert of Extract most of the mutable state of SkShader into a
separate Context object.

[commit-bot: I haz the power, 2014-04-23 19:09:36]

CQ is trying da patch. Follow status at
https://skia-tree-status.appspot.com/cq/bsalomon@google.com/246403013/1

[commit-bot: I haz the power, 2014-04-23 19:11:35]

Change committed as 14328