Implement EGL context priority if supported, use in VrShell

ui/gl/gl_surface_egl.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_SURFACE_EGL_H_
 #define UI_GL_GL_SURFACE_EGL_H_
 
 #if defined(OS_WIN)
 #include <windows.h>
 #endif
@@ skipping 54 matching lines @@
 
   // These aren't particularly tied to surfaces, but since we already
   // have the static InitializeOneOff here, it's easiest to reuse its
   // initialization guards.
   static const char* GetEGLExtensions();
   static bool HasEGLExtension(const char* name);
   static bool IsCreateContextRobustnessSupported();
   static bool IsCreateContextBindGeneratesResourceSupported();
   static bool IsCreateContextWebGLCompatabilitySupported();
   static bool IsEGLSurfacelessContextSupported();
+  static bool IsEGLContextPrioritySupported();
   static bool IsDirectCompositionSupported();
 
  protected:
   ~GLSurfaceEGL() override;
 
   EGLConfig config_ = nullptr;
   GLSurfaceFormat format_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(GLSurfaceEGL);
@@ skipping 112 matching lines @@
   ~SurfacelessEGL() override;
 
  private:
   gfx::Size size_;
   DISALLOW_COPY_AND_ASSIGN(SurfacelessEGL);
 };
 
 }  // namespace gl
 
 #endif  // UI_GL_GL_SURFACE_EGL_H_