Switch DRM platform to using a separate thread

ui/ozone/platform/drm/gpu/proxy_helpers.h

+// 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.
+
+#ifndef UI_OZONE_PLATFORM_DRM_GPU_PROXY_HELPERS_H_
+#define UI_OZONE_PLATFORM_DRM_GPU_PROXY_HELPERS_H_
+
+#include "base/bind.h"
+#include "base/location.h"
+#include "base/memory/ref_counted.h"
+#include "base/thread_task_runner_handle.h"
+
+namespace ui {
+
+namespace internal {
+
+template <typename... Args>
+void PostAsyncTask(
+    const scoped_refptr<base::SingleThreadTaskRunner>& task_runner,
+    const base::Callback<void(Args...)>& callback,
+    Args... args) {
+  task_runner->PostTask(FROM_HERE, base::Bind(callback, args...));
+}
+
+template <typename Functor, typename Type, typename Return, typename... Args>
+void RunWeakPtrMethod(Functor func,
+                      base::WeakPtr<Type> type,
+                      Return* ret,
+                      const Args&... args) {
+  if (type)
+    *ret = ((*type.get()).*func)(args...);
+}
+
+}  // namespace internal
+
+// Posts a task to a different thread and blocks waiting for the task to finish
+// executing.
+void PostSyncTask(
+    const scoped_refptr<base::SingleThreadTaskRunner>& task_runner,
+    const base::Closure& callback);
+
+// Creates a callback that will run |callback| on the calling thread. Useful
+// when posting a task on a different thread and expecting a callback when the
+// task finished (and the callback needs to run on the original thread).
+template <typename... Args>
+base::Callback<void(Args...)> CreateSafeCallback(
+    const base::Callback<void(Args...)>& callback) {
+  return base::Bind(&internal::PostAsyncTask<Args...>,
+                    base::ThreadTaskRunnerHandle::Get(), callback);
+}
+
+// Helper function allowing the caller to post a task to a different thread and
+// calling a base::WeakPtr with a method that returns a value. Since a weak
+// pointer may have expired, this function checks the pointer before attemping
+// to run the method.
+//
+// base::Bind doesn't allow us to do this since the base::WeakPtr specialization
+// allows weak pointers only when the method has a void return.
+//
+// If the weak pointer is valid, |ret| will contain the returned value from
+// type->func(args), otherwise |ret| will not be modified.
+template <typename Functor, typename Type, typename Return, typename... Args>
+base::Closure CreateWeakPtrCallback(Functor func,
+                                    base::WeakPtr<Type> type,
+                                    Return* ret,
+                                    const Args&... args) {
+  return base::Bind(&internal::RunWeakPtrMethod<Functor, Type, Return, Args...>,
+                    func, type, ret, args...);
+}
+
+}  // namespace ui
+
+#endif  // UI_OZONE_PLATFORM_DRM_GPU_PROXY_HELPERS_H_