ozone: Introduce ClientPixmap and ClientPixmapFactory for non-GPU processes.

ui/ozone/public/client_native_pixmap_factory.cc

+// Copyright 2015 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/ozone/public/client_native_pixmap_factory.h"
+
+#include "base/trace_event/trace_event.h"
+#include "ui/ozone/platform_object.h"
+#include "ui/ozone/platform_selection.h"
+
+namespace ui {
+
+namespace {
+
+ClientNativePixmapFactory* g_instance = nullptr;
+
+}  // namespace
+
+// static
+ClientNativePixmapFactory* ClientNativePixmapFactory::GetInstance() {
+  return g_instance;
+}
+
+// static
+void ClientNativePixmapFactory::SetInstance(
+    ClientNativePixmapFactory* instance) {
+  DCHECK(!g_instance);
+  DCHECK(instance);
+  g_instance = instance;
+}
+
+// static
+scoped_ptr<ClientNativePixmapFactory> ClientNativePixmapFactory::Create() {
+  TRACE_EVENT1("ozone", "ClientNativePixmapFactory::Create", "platform",
+               GetOzonePlatformName());
+  return PlatformObject<ClientNativePixmapFactory>::Create();
+}
+
+ClientNativePixmapFactory::ClientNativePixmapFactory() {}
+
+ClientNativePixmapFactory::~ClientNativePixmapFactory() {}

[no sievers, 2015/08/05 18:27:02]

nit: It's a bit of an interesting pattern - the singleton here with the external
scoped ownership. Should we call SetInstance(nullptr) here at least?

[dshwang, 2015/08/05 18:46:34]

This pattern is originated from SurfaceTextureManager and IOSurfaceManager. All
singletons live until the process die. so SetInstance(nullptr) is actually not
needed.
If reveman agree on this idea, I'll add SetInstance(nullptr) to above all
desctuctors in another CLs.

[reveman, 2015/08/05 19:54:03]

The reason for Set/GetInstance is to push the ownership and lifetime management
to content/ instead of having it in ui/. E.g. content/ can create 10
ClientNativePixmapFactory instances but only set one as the current instance.
ui/ doesn't care.

+
+}  // namespace ui