Start making all .cpp files compile-able on all platforms.

src/gpu/gl/win/GrGLCreateNativeInterface_win.cpp

Index: src/gpu/gl/win/GrGLCreateNativeInterface_win.cpp
diff --git a/src/gpu/gl/win/GrGLCreateNativeInterface_win.cpp b/src/gpu/gl/win/GrGLCreateNativeInterface_win.cpp
index c2fcca54692963f9602e001b2b9922dabec27e44..b0eaa548f191d664ffc107c862ae859439ab06b9 100644
--- a/src/gpu/gl/win/GrGLCreateNativeInterface_win.cpp
+++ b/src/gpu/gl/win/GrGLCreateNativeInterface_win.cpp
@@ -5,6 +5,8 @@
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
+#include "SkTypes.h"
+#if defined(SK_BUILD_FOR_WIN32)
 
 #include "gl/GrGLInterface.h"
 #include "gl/GrGLAssembleInterface.h"
@@ -85,3 +87,5 @@ const GrGLInterface* GrGLCreateNativeInterface() {
     }
     return nullptr;
 }
+
+#endif//defined(SK_BUILD_FOR_WIN32)