Improve Sky's Scrollable physics

sky/framework/theme/view-configuration.dart

Index: sky/framework/theme/view-configuration.dart
diff --git a/sky/framework/theme/view-configuration.dart b/sky/framework/theme/view-configuration.dart
index 984c9cab615351cfcd9343d30750d6a4b59f4ded..2b3f895e0715eb480fc9a00584505d300681014c 100644
--- a/sky/framework/theme/view-configuration.dart
+++ b/sky/framework/theme/view-configuration.dart
@@ -5,6 +5,8 @@
 // Modeled after Android's ViewConfiguration:
 // https://github.com/android/platform_frameworks_base/blob/master/core/java/android/view/ViewConfiguration.java
 
-const int kScrollbarSize = 10;
+const int kMaxFlingVelocity = 8000;
+const int kMinFlingVelocity = 50;
 const int kScrollbarFadeDelay = 300;
 const int kScrollbarFadeDuration = 250;
+const int kScrollbarSize = 10;