Add gpu_main_thread_factory.h to expose less of content's guts.

content/browser/gpu/gpu_main_thread_factory.cc

Index: content/browser/gpu/gpu_main_thread_factory.cc
diff --git a/content/browser/gpu/gpu_main_thread_factory.cc b/content/browser/gpu/gpu_main_thread_factory.cc
new file mode 100644
index 0000000000000000000000000000000000000000..06533a1ac434ac1372180cfd5d7578ee21755aff
--- /dev/null
+++ b/content/browser/gpu/gpu_main_thread_factory.cc
@@ -0,0 +1,22 @@
+// Copyright 2017 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 "content/browser/gpu/gpu_main_thread_factory.h"
+
+namespace content {
+namespace {
+
+GpuMainThreadFactoryFunction g_gpu_main_thread_factory = nullptr;
+
+}  // namespace
+
+void RegisterGpuMainThreadFactory(GpuMainThreadFactoryFunction create) {
+  g_gpu_main_thread_factory = create;
+}
+
+GpuMainThreadFactoryFunction GetGpuMainThreadFactory() {
+  return g_gpu_main_thread_factory;
+}
+
+}  // namespace content