Add SlidingAverage to FPSMeter, use for WebVR prediction time

chrome/browser/android/vr_shell/vr_shell_gl.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 CHROME_BROWSER_ANDROID_VR_SHELL_VR_SHELL_GL_H_
 #define CHROME_BROWSER_ANDROID_VR_SHELL_VR_SHELL_GL_H_
 
 #include <memory>
 #include <queue>
 #include <utility>
@@ skipping 25 matching lines @@
 }
 
 namespace gpu {
 struct MailboxHolder;
 }
 
 namespace vr_shell {
 
 class FPSMeter;
 class MailboxToSurfaceBridge;
+class SlidingAverage;
 class UiElement;
 class UiScene;
 class VrBrowserInterface;
 class VrController;
 class VrShell;
 class VrShellRenderer;
 
 struct WebVrBounds {
   WebVrBounds(const gfx::RectF& left,
               const gfx::RectF& right,
@@ skipping 108 matching lines @@
                            gfx::PointF& target_local_point,
                            gfx::Point3F& target_point,
                            float& distance_to_plane) const;
   void HandleControllerInput(const gfx::Vector3dF& head_direction);
   void HandleControllerAppButtonActivity(
       const gfx::Vector3dF& controller_direction);
   void SendGestureToContent(std::unique_ptr<blink::WebInputEvent> event);
   void CreateUiSurface();
   void OnContentFrameAvailable();
   void OnWebVRFrameAvailable();
-  bool GetPixelEncodedFrameIndex(uint16_t* frame_index);
+  int64_t GetPredictedFrameTimeNanos();
 
   void OnVSync();
 
   // VRVSyncProvider
   void GetVSync(const GetVSyncCallback& callback) override;
 
   void ForceExitVr();
 
   void SendVSync(base::TimeDelta time, const GetVSyncCallback& callback);
 
@@ skipping 81 matching lines @@
 
   uint8_t frame_index_ = 0;
   // Larger than frame_index_ so it can be initialized out-of-band.
   uint16_t last_frame_index_ = -1;
 
   // Attributes for gesture detection while holding app button.
   gfx::Vector3dF controller_start_direction_;
 
   std::unique_ptr<FPSMeter> fps_meter_;
 
+  std::unique_ptr<SlidingAverage> webvr_js_time_;
+  std::unique_ptr<SlidingAverage> webvr_render_time_;
+
   gfx::Point3F pointer_start_;
 
   base::WeakPtrFactory<VrShellGl> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(VrShellGl);
 };
 
 }  // namespace vr_shell
 
 #endif  // CHROME_BROWSER_ANDROID_VR_SHELL_VR_SHELL_GL_H_