Adds in-out easing type.

chrome/browser/android/vr_shell/easing.h

Index: chrome/browser/android/vr_shell/easing.h
diff --git a/chrome/browser/android/vr_shell/easing.h b/chrome/browser/android/vr_shell/easing.h
index 2ef0617cc686822193d553f50e9e0b4563690fee..069815401f11f99cbb799cf0c8a4b7c9fb7ebe62 100644
--- a/chrome/browser/android/vr_shell/easing.h
+++ b/chrome/browser/android/vr_shell/easing.h
@@ -16,6 +16,7 @@ enum EasingType {
   CUBICBEZIER,
   EASEIN,
   EASEOUT,
+  EASEINOUT,
 };
 
 // Abstract base class for custom interpolators, mapping linear input between
@@ -78,6 +79,17 @@ class EaseOut : public Easing {
   DISALLOW_COPY_AND_ASSIGN(EaseOut);
 };
 
+// Starts with EaseIn and finishes with EaseOut.
+class EaseInOut : public Easing {
+ public:
+  explicit EaseInOut(double power);
+  double CalculateValueImpl(double input) override;
+
+ private:
+  EaseIn ease_in_;
+  DISALLOW_COPY_AND_ASSIGN(EaseInOut);
+};
+
 }  // namespace easing
 }  // namespace vr_shell