Changing animate to beginFrame and use struct rather than naked double to allow extension.

Source/core/page/AutoscrollController.h

Index: Source/core/page/AutoscrollController.h
diff --git a/Source/core/page/AutoscrollController.h b/Source/core/page/AutoscrollController.h
index 62f7fd6a3bb2b88de4e08589016120646b081ee4..07b8422e3863228af388d98db28c90363a58bd95 100644
--- a/Source/core/page/AutoscrollController.h
+++ b/Source/core/page/AutoscrollController.h
@@ -27,6 +27,7 @@
 #define AutoscrollController_h
 
 #include "platform/geometry/IntPoint.h"
+#include "public/platform/WebFrameTime.h"
 #include "wtf/PassOwnPtr.h"
 
 namespace WebCore {
@@ -55,7 +56,7 @@ class AutoscrollController {
 public:
     static PassOwnPtr<AutoscrollController> create(Page&);
 
-    void animate(double monotonicFrameBeginTime);
+    void animate(blink::WebFrameTime);
     bool autoscrollInProgress() const;
     bool autoscrollInProgress(const RenderBox*) const;
     bool panScrollInProgress() const;