Implement EGL context priority if supported, use in VrShell

chrome/browser/android/vr_shell/vr_shell_gl.cc

Index: chrome/browser/android/vr_shell/vr_shell_gl.cc
diff --git a/chrome/browser/android/vr_shell/vr_shell_gl.cc b/chrome/browser/android/vr_shell/vr_shell_gl.cc
index 452f39debd789433d5143a72349ad28b42af476d..bce31e603bd51ab49567774335607577eb5454c1 100644
--- a/chrome/browser/android/vr_shell/vr_shell_gl.cc
+++ b/chrome/browser/android/vr_shell/vr_shell_gl.cc
@@ -277,8 +277,10 @@ void VrShellGl::InitializeGl(gfx::AcceleratedWidget window) {
     ForceExitVr();
     return;
   }
-  context_ = gl::init::CreateGLContext(nullptr, surface_.get(),
-                                       gl::GLContextAttribs());
+
+  gl::GLContextAttribs attribs;
+  attribs.context_priority = gl::ContextPriorityHigh;
+  context_ = gl::init::CreateGLContext(nullptr, surface_.get(), attribs);
   if (!context_.get()) {
     LOG(ERROR) << "gl::init::CreateGLContext failed";
     ForceExitVr();