Adds a GrGLPathRendering class that wraps the NV_path_rendering
extension and manages its various API versions. It also provides
backup implementations when certain NVpr methods from later API
versions are not present on the current system.

R=bsalomon@google.com, kkinnunen@nvidia.com, markkilgard@gmail.com

Author: cdalton@nvidia.com

Review URL: https://codereview.chromium.org/437473002
diff --git a/include/gpu/gl/GrGLFunctions.h b/include/gpu/gl/GrGLFunctions.h
index 584ad27..84b6c29 100644
--- a/include/gpu/gl/GrGLFunctions.h
+++ b/include/gpu/gl/GrGLFunctions.h
@@ -245,11 +245,12 @@
     typedef GrGLvoid (GR_GL_FUNCTION_TYPE* GrGLCoverStrokePathProc)(GrGLuint name, GrGLenum coverMode);
     typedef GrGLvoid (GR_GL_FUNCTION_TYPE* GrGLCoverFillPathInstancedProc)(GrGLsizei numPaths, GrGLenum pathNameType, const GrGLvoid *paths, GrGLuint pathBase, GrGLenum coverMode, GrGLenum transformType, const GrGLfloat *transformValues);
     typedef GrGLvoid (GR_GL_FUNCTION_TYPE* GrGLCoverStrokePathInstancedProc)(GrGLsizei numPaths, GrGLenum pathNameType, const GrGLvoid *paths, GrGLuint pathBase, GrGLenum coverMode, GrGLenum transformType, const GrGLfloat* transformValues);
+    // NV_path_rendering v1.2
     typedef GrGLvoid (GR_GL_FUNCTION_TYPE* GrGLStencilThenCoverFillPathProc)(GrGLuint path, GrGLenum fillMode, GrGLuint mask, GrGLenum coverMode);
     typedef GrGLvoid (GR_GL_FUNCTION_TYPE* GrGLStencilThenCoverStrokePathProc)(GrGLuint path, GrGLint reference, GrGLuint mask, GrGLenum coverMode);
     typedef GrGLvoid (GR_GL_FUNCTION_TYPE* GrGLStencilThenCoverFillPathInstancedProc)(GrGLsizei numPaths, GrGLenum pathNameType, const GrGLvoid *paths, GrGLuint pathBase, GrGLenum fillMode, GrGLuint mask, GrGLenum coverMode, GrGLenum transformType, const GrGLfloat *transformValues);
     typedef GrGLvoid (GR_GL_FUNCTION_TYPE* GrGLStencilThenCoverStrokePathInstancedProc)(GrGLsizei numPaths, GrGLenum pathNameType, const GrGLvoid *paths, GrGLuint pathBase, GrGLint reference, GrGLuint mask, GrGLenum coverMode, GrGLenum transformType, const GrGLfloat *transformValues);
-
+    // NV_path_rendering v1.3
     typedef GrGLvoid (GR_GL_FUNCTION_TYPE* GrGLProgramPathFragmentInputGenProc)(GrGLuint program, GrGLint location, GrGLenum genMode, GrGLint components,const GrGLfloat *coeffs);
 }  // extern "C"