Adds in-out easing type.

chrome/browser/android/vr_shell/easing.cc

 // 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.
 
 #include "chrome/browser/android/vr_shell/easing.h"
 
 #include <cmath>
 
 #include "base/logging.h"
 
@@ skipping 15 matching lines @@
 EaseIn::EaseIn(double power) : power_(power) {}
 double EaseIn::CalculateValueImpl(double state) {
   return pow(state, power_);
 }
 
 EaseOut::EaseOut(double power) : power_(power) {}
 double EaseOut::CalculateValueImpl(double state) {
   return 1.0 - pow(1.0 - state, power_);
 }
 
+EaseInOut::EaseInOut(double power) : ease_in_(power) {}
+double EaseInOut::CalculateValueImpl(double state) {
+  if (state < 0.5) {
+    return ease_in_.CalculateValueImpl(state * 2) / 2;
+  } else {
+    return 1.0 - ease_in_.CalculateValueImpl((1.0 - state) * 2) / 2;
+  }
+}
+
 double Linear::CalculateValueImpl(double state) {
   return state;
 }
 
 }  // namespace easing
 }  // namespace vr_shell