Make the drawer, popup menus, dialogs, and settings page scrollable.

sky/engine/core/painting/OffsetBase.dart

Index: sky/engine/core/painting/OffsetBase.dart
diff --git a/sky/engine/core/painting/OffsetBase.dart b/sky/engine/core/painting/OffsetBase.dart
index 1f5a0cb5c90216e75d9598a2c8d6461d7151ad0a..8697abdbbcaf81e76c1bce49190596b7c3b7169d 100644
--- a/sky/engine/core/painting/OffsetBase.dart
+++ b/sky/engine/core/painting/OffsetBase.dart
@@ -12,6 +12,11 @@ abstract class OffsetBase {
 
   bool get isInfinite => _dx >= double.INFINITY || _dy >= double.INFINITY;
 
+  bool operator <(OffsetBase other) => _dx < other._dx && _dy < other._dy;
+  bool operator <=(OffsetBase other) => _dx <= other._dx && _dy <= other._dy;
+  bool operator >(OffsetBase other) => _dx > other._dx && _dy > other._dy;
+  bool operator >=(OffsetBase other) => _dx > other._dx && _dy >= other._dy;
+
   bool operator ==(other) {
     return other is OffsetBase &&
            other.runtimeType == runtimeType &&