Implement InstanceMirror.== in dart2js and InstanceMirror.hashCode in the VM and …

runtime/lib/mirrors_impl.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 // VM-specific implementation of the dart:mirrors library.
 
 import "dart:collection";
 
 // These values are allowed to be passed directly over the wire.
 bool _isSimpleValue(var value) {
@@ skipping 265 matching lines @@
     return _invokeOnClosure(reflectee, invocation);
   }
 
   String toString() => 'InstanceMirror on ${Error.safeToString(_reflectee)}';
 
   bool operator ==(other) {
     return other is _LocalInstanceMirrorImpl &&
            identical(_reflectee, other._reflectee);
   }
 
-  // TODO(12909): Use the reflectee's identity hash.
-  int get hashCode => _reflectee.hashCode;
+  int get hashCode {
+    // If the reflectee is a double or bignum, use the base hashCode to preserve
+    // the illusion that boxed numbers with the same value are identical. If the
+    // reflectee is a Smi, use the base hashCode because Object.hashCode does
+    // not work for non-heap objects. Otherwise, use Object.hashCode to maintain
+    // correctness even if a user-defined hashCode returns different values for
+    // successive invocations.
+    var h = _reflectee is num ? _reflectee.hashCode : _identityHash(_reflectee);
+    // Avoid hash collisions with the reflectee. This constant is in Smi range
+    // and happens to be the inner padding from RFC 2104.
+    return h ^ 0x36363636;
+  }
+
+  static _identityHash(reflectee)
+      native "InstanceMirror_identityHash";
 
   _invoke(reflectee, functionName, positionalArguments)
       native 'InstanceMirror_invoke';
 
   _invokeGetter(reflectee, getterName)
       native 'InstanceMirror_invokeGetter';
 
   _invokeSetter(reflectee, setterName, value)
       native 'InstanceMirror_invokeSetter';
 
@@ skipping 997 matching lines @@
     if (typeMirror == null) {
       typeMirror = makeLocalTypeMirror(key);
       _instanitationCache[key] = typeMirror;
       if (typeMirror is ClassMirror && !typeMirror._isGeneric) {
         _declarationCache[key] = typeMirror;
       }
     }
     return typeMirror;
   }
 }