Sped up hashCode by removing megamorphic call to _identityHashCode.

runtime/lib/object_patch.dart

Index: runtime/lib/object_patch.dart
diff --git a/runtime/lib/object_patch.dart b/runtime/lib/object_patch.dart
index 7c4f5f54f629029e3f120ac9cbc7f0eb33071990..69723b38039f46b3eec4b1f5770768a6eea5b6eb 100644
--- a/runtime/lib/object_patch.dart
+++ b/runtime/lib/object_patch.dart
@@ -15,21 +15,23 @@ patch class Object {
   static _getHash(obj) native "Object_getHash";
   static _setHash(obj, hash) native "Object_setHash";
 
-  /* patch */ int get hashCode => _identityHashCode;
-
-  int get _identityHashCode {
-    var result = _getHash(this);
+  // Shared static implentation for hashCode and _identityHashCode.
+  static int _objectHashCode(obj) {
+    var result = _getHash(obj);
     if (result == 0) {
       // We want the hash to be a Smi value greater than 0.
       result = _hashCodeRnd.nextInt(0x40000000);
       while (result == 0) {
         result = _hashCodeRnd.nextInt(0x40000000);
       }
-      _setHash(this, result);
+      _setHash(obj, result);
     }
     return result;
   }
 
+  /* patch */ int get hashCode => _objectHashCode(this);
+  int get _identityHashCode => _objectHashCode(this);
+
   /* patch */ String toString() native "Object_toString";
   // A statically dispatched version of Object.toString.
   static String _toString(obj) native "Object_toString";