Correct bottom overscroll in VariableHeightScrollable

sky/sdk/lib/widgets/scrollable.dart

Index: sky/sdk/lib/widgets/scrollable.dart
diff --git a/sky/sdk/lib/widgets/scrollable.dart b/sky/sdk/lib/widgets/scrollable.dart
index 807bd26a963dfc019d30154d001e211a8eb31674..8fc480f7b2ea472d371205ed951f7e0d7ddc366e 100644
--- a/sky/sdk/lib/widgets/scrollable.dart
+++ b/sky/sdk/lib/widgets/scrollable.dart
@@ -14,6 +14,7 @@ import 'package:sky/widgets/material.dart';
 const double _kMillisecondsPerSecond = 1000.0;
 
 double _velocityForFlingGesture(double eventVelocity) {
+  // eventVelocity is pixels/second, config min,max limits are pixels/ms

[Chinmay, 2015/07/14 20:59:08]

I am not sure why we do this at all. The input event from the platform returns
the velocity in pixels/second. We convert to pixels/ms here and then back to
pixels/second in the bounded behavior. The two conversions are redundant.

   return eventVelocity.clamp(-config.kMaxFlingVelocity, config.kMaxFlingVelocity) /
     _kMillisecondsPerSecond;
 }