added support for glMinSampleShading

src/gpu/gl/GrGLTestInterface.h

Index: src/gpu/gl/GrGLTestInterface.h
diff --git a/src/gpu/gl/GrGLTestInterface.h b/src/gpu/gl/GrGLTestInterface.h
index f8c5801a7f844039149ecd903b55041cfda7b84d..6af71feee23d464196f5d00c8428c528dd2f5789 100644
--- a/src/gpu/gl/GrGLTestInterface.h
+++ b/src/gpu/gl/GrGLTestInterface.h
@@ -113,6 +113,7 @@ public:
     virtual GrGLvoid* mapBufferRange(GrGLenum target, GrGLintptr offset, GrGLsizeiptr length, GrGLbitfield access) { return nullptr; }
     virtual GrGLvoid* mapBufferSubData(GrGLuint target, GrGLintptr offset, GrGLsizeiptr size, GrGLenum access) { return nullptr; }
     virtual GrGLvoid* mapTexSubImage2D(GrGLenum target, GrGLint level, GrGLint xoffset, GrGLint yoffset, GrGLsizei width, GrGLsizei height, GrGLenum format, GrGLenum type, GrGLenum access) { return nullptr; }
+    virtual GrGLvoid minSampleShading(GrGLfloat value) {}    
     virtual GrGLvoid pixelStorei(GrGLenum pname, GrGLint param) {}
     virtual GrGLvoid popGroupMarker() {}
     virtual GrGLvoid pushGroupMarker(GrGLsizei length, const char* marker) {}