Move SkGLContext and some GrGLInterface implementations to skgputest module

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 6af71feee23d464196f5d00c8428c528dd2f5789..5ce48664baeea1c9bc6e2b662f7b7701c33c4594 100644
--- a/src/gpu/gl/GrGLTestInterface.h
+++ b/src/gpu/gl/GrGLTestInterface.h
@@ -11,6 +11,10 @@
 #include "gl/GrGLInterface.h"
 #include "GrGLDefines.h"
 
+/**
+ * Base class for interfaces used for Skia testing. We would like to move this to tools/gpu/gl
+ * when Chromium is no longer using GrGLCreateNullInterface in its unit testing.
+ */
 class GrGLTestInterface : public GrGLInterface {
 public:
     virtual GrGLvoid activeTexture(GrGLenum texture) {}