compositor: Fix compositor_unittests build on Linux.

ui/gfx/compositor/test_compositor_host_linux.cc

Index: ui/gfx/compositor/test_compositor_host_linux.cc
diff --git a/ui/gfx/compositor/test_compositor_host_linux.cc b/ui/gfx/compositor/test_compositor_host_linux.cc
new file mode 100644
index 0000000000000000000000000000000000000000..034ddfb03a7ea4bcf4af2e8eb476b4aaa42bd4ac
--- /dev/null
+++ b/ui/gfx/compositor/test_compositor_host_linux.cc
@@ -0,0 +1,14 @@
+// Copyright (c) 2011 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.
+
+#include "ui/gfx/compositor/test_compositor_host.h"
+
+namespace ui {
+
+// static
+TestCompositorHost* TestCompositorHost::Create(const gfx::Rect& bounds) {
+  return NULL;
+}
+
+}  // namespace ui