Refactors animation to allow for cleaner subclassing. I'm doing this

app/tween.h

Index: app/tween.h
diff --git a/app/tween.h b/app/tween.h
new file mode 100644
index 0000000000000000000000000000000000000000..41785ef62b17e2f61c125f50f9071a542e50bd12
--- /dev/null
+++ b/app/tween.h
@@ -0,0 +1,43 @@
+// Copyright (c) 2010 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 APP_TWEEN_H_
+#define APP_TWEEN_H_
+
+#include "base/logging.h"
+
+namespace gfx {
+class Rect;
+}
+
+class Tween {
+ public:
+  enum Type {
+    LINEAR,        // Linear.
+    EASE_OUT,      // Fast in, slow out (default).
+    EASE_IN,       // Slow in, fast out.
+    EASE_IN_OUT,   // Slow in and out, fast in the middle.
+    FAST_IN_OUT,   // Fast in and out, slow in the middle.
+    EASE_OUT_SNAP, // Fast in, slow out, snap to final value.
+    ZERO,          // Returns a value of 0 always.
+  };
+
+  // Returns the value based on the tween type. |state| is from 0-1.
+  static double CalculateValue(Type type, double state);
+
+  // Conveniences for getting a value between a start and end point.
+  static double ValueBetween(double value, double start, double target);
+  static int ValueBetween(double value, int start, int target);
+  static gfx::Rect ValueBetween(double value,
+                                const gfx::Rect& start_bounds,
+                                const gfx::Rect& target_bounds);
+
+ private:
+  Tween();
+  ~Tween();
+
+  DISALLOW_COPY_AND_ASSIGN(Tween);
+};
+
+#endif  // APP_TWEEN_H_