Move GL one-off initialization code.

ui/gl/init/gl_initializer.h

+// Copyright 2016 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_GL_INIT_GL_INITIALIZER_H_
+#define UI_GL_INIT_GL_INITIALIZER_H_
+
+namespace gl {
+namespace init {
+
+// Performs platform dependent one-off GL initialization, calling into the
+// appropriate GLSurface code to initialize it. To perform one-off GL
+// initialization you should use InitializeGLOneOff() or for tests possibly
+// InitializeGLOneOffImplementation() instead of this.
+bool InitializeGLOneOffPlatform();
+
+}  // namespace init
+}  // namespace gl
+
+#endif  // UI_GL_INIT_GL_INITIALIZER_H_