Implement hashCode on objects stored in a set or used as map keys.

dart/sdk/lib/_internal/compiler/implementation/ssa/types.dart

Index: dart/sdk/lib/_internal/compiler/implementation/ssa/types.dart
diff --git a/dart/sdk/lib/_internal/compiler/implementation/ssa/types.dart b/dart/sdk/lib/_internal/compiler/implementation/ssa/types.dart
index 38cc81253bc036dd348448bbf265c91e368f19f3..fd8d66058ae0b8dee096e862189c13abd526d705 100644
--- a/dart/sdk/lib/_internal/compiler/implementation/ssa/types.dart
+++ b/dart/sdk/lib/_internal/compiler/implementation/ssa/types.dart
@@ -533,12 +533,14 @@ class HBoundedType extends HType {
     return isIndexablePrimitive(compiler);
   }
 
-  bool operator ==(HType other) {
+  bool operator ==(other) {
     if (other is !HBoundedType) return false;
     HBoundedType bounded = other;
     return mask == bounded.mask;
   }
 
+  int get hashCode => mask.hashCode;
+
   String toString() {
     return 'BoundedType(mask=$mask)';
   }