Revert of Revert of ozone: gpu: Add plumbing for platform-specific gpu messaging

ui/ozone/public/gpu_platform_support_host.h

+// Copyright 2014 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_OZONE_PUBLIC_GPU_PLATFORM_SUPPORT_HOST_H_
+#define UI_OZONE_PUBLIC_GPU_PLATFORM_SUPPORT_HOST_H_
+
+#include "ipc/ipc_listener.h"
+#include "ipc/ipc_sender.h"
+#include "ui/ozone/ozone_base_export.h"
+
+namespace ui {
+
+// Platform-specific object to support a GPU process host.
+//
+// ChromeOS on bare hardware will do display configuration and cursor
+// movement from the GPU process. This provides a conduit for the
+// messages needed to make this work.
+//
+// Under X11, we don't need any GPU messages for display configuration.
+// That's why there's no real functionality here: it's purely mechanism
+// to support additional messages needed by specific platforms.
+class OZONE_BASE_EXPORT GpuPlatformSupportHost : public IPC::Listener {
+ public:
+  GpuPlatformSupportHost();
+  virtual ~GpuPlatformSupportHost();
+
+  // Called when the GPU process is spun up & channel established.
+  virtual void OnChannelEstablished(int host_id, IPC::Sender* sender) = 0;
+
+  // Called when the GPU process is destroyed.
+  virtual void OnChannelDestroyed(int host_id) = 0;
+};
+
+// create a stub implementation.
+OZONE_BASE_EXPORT GpuPlatformSupportHost* CreateStubGpuPlatformSupportHost();
+
+}  // namespace ui
+
+#endif  // UI_OZONE_PUBLIC_GPU_PLATFORM_SUPPORT_HOST_H_