Add SK_API to GrGLExtensions

include/gpu/gl/GrGLExtensions.h

Index: include/gpu/gl/GrGLExtensions.h
diff --git a/include/gpu/gl/GrGLExtensions.h b/include/gpu/gl/GrGLExtensions.h
index dbfc3be45e7fdb1a94f3802622d8cbf348a972b7..89adadfc48ec558d19a71c3ee056387da8b22b9b 100644
--- a/include/gpu/gl/GrGLExtensions.h
+++ b/include/gpu/gl/GrGLExtensions.h
@@ -19,7 +19,7 @@ struct GrGLInterface;
  * queried. It supports both glGetString- and glGetStringi-style extension string APIs and will
  * use the latter if it is available.
  */
-class GrGLExtensions {
+class SK_API GrGLExtensions {
 public:
     GrGLExtensions() : fInitialized(false), fStrings(SkNEW(SkTArray<SkString>)) {}