VM library tweaks to avoid megamorphic calls in dart2js

runtime/lib/integers.dart

Index: runtime/lib/integers.dart
diff --git a/runtime/lib/integers.dart b/runtime/lib/integers.dart
index 9192b28bfa2592d5412ecb1b0e16446bb9d68dbf..45500d6dc21ecd5b3af28a6ae3585ddfa3a9a558 100644
--- a/runtime/lib/integers.dart
+++ b/runtime/lib/integers.dart
@@ -410,9 +410,8 @@ class _Smi extends _IntegerImplementation implements int {
     throw new UnsupportedError(
         "_Smi can only be allocated by the VM");
   }
-  int get _identityHashCode {
-    return this;
-  }
+  int get _identityHashCode => this;
+  int get hashCode => this;
   int operator ~() native "Smi_bitNegate";
   int get bitLength native "Smi_bitLength";
 
@@ -608,9 +607,8 @@ class _Mint extends _IntegerImplementation implements int {
     throw new UnsupportedError(
         "_Mint can only be allocated by the VM");
   }
-  int get _identityHashCode {
-    return this;
-  }
+  int get _identityHashCode => this;
+  int get hashCode => this;
   int operator ~() native "Mint_bitNegate";
   int get bitLength native "Mint_bitLength";