Add ability to wire up sharelist in glcontext creation

include/gpu/gl/SkGLContext.h

Index: include/gpu/gl/SkGLContext.h
diff --git a/include/gpu/gl/SkGLContext.h b/include/gpu/gl/SkGLContext.h
index 77fd325dd853e9eac8d061316134474258135071..966ad81768246ae469d14fd32200ac7eae05a705 100644
--- a/include/gpu/gl/SkGLContext.h
+++ b/include/gpu/gl/SkGLContext.h
@@ -120,7 +120,8 @@ private:
  * Otherwise, the default implementation for the platform should be compiled in
  * the library.

[bsalomon, 2016/01/19 22:00:57]

Should comment on shareList. Also, name doesn't seem intuitive to me as it's not
a list.

Also, the param must be a context previously returned by
SkCreatePlatformGLContext. Otherwise it may be of the a unexpected subclass
(angle, osmesa, ...) .

[joshualitt, 2016/01/20 14:36:56]

Acknowledged.

  */
-SK_API SkGLContext* SkCreatePlatformGLContext(GrGLStandard forcedGpuAPI);
+SK_API SkGLContext* SkCreatePlatformGLContext(GrGLStandard forcedGpuAPI,
+                                              SkGLContext* shareList = nullptr);
 
 /**
  * Helper macros for using the GL context through the GrGLInterface. Example: