Use OS_LINUX instead of USE_OZONE in ui/gfx/ when possible

ui/gfx/mojo/buffer_types_struct_traits.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_GFX_MOJO_BUFFER_TYPES_STRUCT_TRAITS_H_
 #define UI_GFX_MOJO_BUFFER_TYPES_STRUCT_TRAITS_H_
 
 #include "ui/gfx/buffer_types.h"
 #include "ui/gfx/mojo/buffer_types.mojom.h"
 
@@ skipping 217 matching lines @@
 template <>
 struct StructTraits<gfx::mojom::NativePixmapHandleDataView,
                     gfx::NativePixmapHandle> {
   using PixmapHandleFdList = std::vector<mojo::ScopedHandle>;
 
   static void* SetUpContext(const gfx::NativePixmapHandle& handle);
   static void TearDownContext(const gfx::NativePixmapHandle& handle,
                               void* context);
 
   static bool IsNull(const gfx::NativePixmapHandle& handle) {
-#if defined(USE_OZONE)
+#if defined(OS_LINUX)
     return false;
 #else
-    // NativePixmapHandle are not used on non-ozone platforms.
+    // NativePixmapHandle are not used on non-linux platforms.
     return true;
 #endif
   }
   static PixmapHandleFdList fds(const gfx::NativePixmapHandle& pixmap_handle,
                                 void* context);
 
   static const std::vector<gfx::NativePixmapPlane>& planes(
       const gfx::NativePixmapHandle& pixmap_handle) {
     return pixmap_handle.planes;
   }
@@ skipping 23 matching lines @@
   static const gfx::NativePixmapHandle& native_pixmap_handle(
       const gfx::GpuMemoryBufferHandle& handle);
   static mojo::ScopedHandle mach_port(const gfx::GpuMemoryBufferHandle& handle);
   static bool Read(gfx::mojom::GpuMemoryBufferHandleDataView data,
                    gfx::GpuMemoryBufferHandle* handle);
 };
 
 }  // namespace mojo
 
 #endif  // UI_GFX_MOJO_BUFFER_TYPES_STRUCT_TRAITS_H_