Add support for bounds animations

ui/gfx/animation/tween.h

Index: ui/gfx/animation/tween.h
diff --git a/ui/gfx/animation/tween.h b/ui/gfx/animation/tween.h
index 3be0e95286242fd708e3921323ae7fe2355f5147..15107adf592c2e37be3ee92154e9d60d820682c2 100644
--- a/ui/gfx/animation/tween.h
+++ b/ui/gfx/animation/tween.h
@@ -9,6 +9,7 @@
 #include "third_party/skia/include/core/SkColor.h"
 #include "ui/gfx/animation/animation_export.h"
 #include "ui/gfx/geometry/rect.h"
+#include "ui/gfx/geometry/size_f.h"
 #include "ui/gfx/transform.h"
 
 namespace base {
@@ -72,6 +73,10 @@ class ANIMATION_EXPORT Tween {
       const gfx::Transform& start_transform,
       const gfx::Transform& target_transform);
 
+  static gfx::SizeF SizeValueBetween(double value,
+                                     const gfx::SizeF& start_size,
+                                     const gfx::SizeF& target_size);
+
  private:
   Tween();
   ~Tween();