Replace uses of GR_DEBUG by SK_DEBUG.

src/gpu/gr_unittests.cpp

Index: src/gpu/gr_unittests.cpp
diff --git a/src/gpu/gr_unittests.cpp b/src/gpu/gr_unittests.cpp
index a6a43c4f27b4491a8e8a64d19d66f37bf41c9b04..f586a94be757816c5bb191e8b768a69a6656e8f7 100644
--- a/src/gpu/gr_unittests.cpp
+++ b/src/gpu/gr_unittests.cpp
@@ -17,7 +17,7 @@ void gr_run_unittests();
 // If we aren't inheriting these as #defines from elsewhere,
 // clang demands they be declared before we #include the template
 // that relies on them.
-#if GR_DEBUG
+#ifdef SK_DEBUG
 static bool LT(const int& elem, int value) {
     return elem < value;
 }