Add ShareGroup stub

gpu/command_buffer/client/share_group.cc

Index: gpu/command_buffer/client/share_group.cc
diff --git a/gpu/command_buffer/client/share_group.cc b/gpu/command_buffer/client/share_group.cc
new file mode 100644
index 0000000000000000000000000000000000000000..3e3b7e601eb49408ea0733e778bafea6e8e8487e
--- /dev/null
+++ b/gpu/command_buffer/client/share_group.cc
@@ -0,0 +1,20 @@
+// Copyright (c) 2012 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 "../client/share_group.h"
+#include "../common/logging.h"
+
+namespace gpu {
+namespace gles2 {
+
+ShareGroup::ShareGroup() {
+  GPU_CHECK(ShareGroup::ImplementsThreadSafeReferenceCounting());
+}
+
+ShareGroup::~ShareGroup() {
+}
+
+}  // namespace gles2
+}  // namespace gpu
+