[vr] Add a frame rate counter for the vr UI

chrome/browser/android/vr_shell/vr_shell_gl.h

Index: chrome/browser/android/vr_shell/vr_shell_gl.h
diff --git a/chrome/browser/android/vr_shell/vr_shell_gl.h b/chrome/browser/android/vr_shell/vr_shell_gl.h
index 68d7a5cd4683ade63a5360d45440f80da8d8e8c1..1359ed71c4e5297ec5f013a92ed04912cd78cbb5 100644
--- a/chrome/browser/android/vr_shell/vr_shell_gl.h
+++ b/chrome/browser/android/vr_shell/vr_shell_gl.h
@@ -43,6 +43,7 @@ struct MailboxHolder;
 
 namespace vr_shell {
 
+class FPSMeter;
 class MailboxToSurfaceBridge;
 class UiScene;
 class VrController;
@@ -239,6 +240,8 @@ class VrShellGl : public device::mojom::VRVSyncProvider {
   // Attributes for gesture detection while holding app button.
   gvr::Vec3f controller_start_direction_;
 
+  std::unique_ptr<FPSMeter> fps_meter_;
+
   base::WeakPtrFactory<VrShellGl> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(VrShellGl);