Adds in-out easing type.

chrome/browser/android/vr_shell/easing.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_EASING_H_
 #define CHROME_BROWSER_ANDROID_VR_SHELL_EASING_H_
 
 #include "base/macros.h"
 #include "ui/gfx/geometry/cubic_bezier.h"
 
 namespace vr_shell {
 namespace easing {
 
 enum EasingType {
   LINEAR = 0,
   CUBICBEZIER,
   EASEIN,
-  EASEOUT
+  EASEOUT,
+  EASEINOUT

[cjgrant, 2017/02/16 15:10:25]

nit: Should have a comma as well.
https://engdoc.corp.google.com/eng/doc/devguide/cpp/styleguide.shtml?cl=head#...

[tiborg, 2017/02/16 18:39:33]

Done.

 };
 
 // Abstract base class for custom interpolators, mapping linear input between
 // 0 and 1 to custom values between those two points.
 class Easing {
  public:
   // Compute an output value, given an input between 0 and 1. Output will
   // equal input at (at least) points 0 and 1.
   double CalculateValue(double input);
   virtual ~Easing() {}
@@ skipping 42 matching lines @@
 class EaseOut : public Easing {
  public:
   explicit EaseOut(double power);
   double CalculateValueImpl(double input) override;
 
  private:
   double power_;
   DISALLOW_COPY_AND_ASSIGN(EaseOut);
 };
 
+// Behaves like EaseIn for inputs smaller 0.5 and like EaseOut otherwise.

[cjgrant, 2017/02/16 15:10:25]

s/smaller/smaller than/.  But I found the comment a bit confusing, in that it
sounded like a different curve for small movements.  Maybe just stay "Starts
with EaseIn and finishes with EaseOut.", if you think that's better.

[tiborg, 2017/02/16 18:39:33]

Done.

+class EaseInOut : public Easing {
+ public:
+  explicit EaseInOut(double power);
+  double CalculateValueImpl(double input) override;
+
+ private:
+  EaseIn ease_in_;
+  EaseOut ease_out_;
+  DISALLOW_COPY_AND_ASSIGN(EaseInOut);
+};
+
 }  // namespace easing
 }  // namespace vr_shell
 
 #endif  // CHROME_BROWSER_ANDROID_VR_SHELL_EASING_H_