Implement EGL context priority if supported, use in VrShell

ui/gl/gl_context.h

 // Copyright (c) 2012 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_GL_CONTEXT_H_
 #define UI_GL_GL_CONTEXT_H_
 
 #include <memory>
 #include <string>
 #include <vector>
@@ skipping 21 matching lines @@
 class DebugGLApi;
 struct DriverGL;
 class GLApi;
 class GLSurface;
 class GPUTiming;
 class GPUTimingClient;
 struct GLVersionInfo;
 class RealGLApi;
 class TraceGLApi;
 
+enum ContextPriority {
+  ContextPriorityLow,
+  ContextPriorityMedium,
+  ContextPriorityHigh
+};
+
 struct GLContextAttribs {
   GpuPreference gpu_preference = PreferIntegratedGpu;
   bool bind_generates_resource = true;
   bool webgl_compatibility_context = false;
   bool global_texture_share_group = false;
   int client_major_es_version = 3;
   int client_minor_es_version = 0;
+  ContextPriority context_priority = ContextPriorityMedium;
 };
 
 // Encapsulates an OpenGL context, hiding platform specific management.
 class GL_EXPORT GLContext : public base::RefCounted<GLContext> {
  public:
   explicit GLContext(GLShareGroup* share_group);
 
   // Initializes the GL context to be compatible with the given surface. The GL
   // context can be made with other surface's of the same type. The compatible
   // surface is only needed for certain platforms like WGL, OSMesa and GLX. It
@@ skipping 181 matching lines @@
 // scoped_refptr containing the initialized GLContext or nullptr if
 // initialization fails.
 GL_EXPORT scoped_refptr<GLContext> InitializeGLContext(
     scoped_refptr<GLContext> context,
     GLSurface* compatible_surface,
     const GLContextAttribs& attribs);
 
 }  // namespace gl
 
 #endif  // UI_GL_GL_CONTEXT_H_