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

sdk/lib/_internal/lib/js_mirrors.dart

Index: sdk/lib/_internal/lib/js_mirrors.dart
diff --git a/sdk/lib/_internal/lib/js_mirrors.dart b/sdk/lib/_internal/lib/js_mirrors.dart
index d5db7e5f505c54dafa04c3d37eddaf99847fd051..8911a689052d16f099f2a8ed153d56ba3b311d55 100644
--- a/sdk/lib/_internal/lib/js_mirrors.dart
+++ b/sdk/lib/_internal/lib/js_mirrors.dart
@@ -677,6 +677,26 @@ class JsInstanceMirror extends JsObjectMirror implements InstanceMirror {
     return JSInvocationMirror.invokeFromMirror(invocation, reflectee);
   }
 
+  operator ==(other) {
+    return other is JsInstanceMirror &&
+           identical(reflectee, other.reflectee);
+  }
+
+  int get hashCode {
+    // If the reflectee is a built-in type, use the base-level hashCode to
+    // preserve the illusion that, e.g. doubles, with the same value are
+    // identical. Otherwise, use the primitive identity hash to maintain
+    // correctness even if a user-defined hashCode returns different values for
+    // successive invocations.
+    var h = ((JS('bool', 'typeof # != "object"', reflectee)) || 
+             (reflectee == null))
+        ? reflectee.hashCode
+        : Primitives.objectHashCode(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;
+  }
+
   String toString() => 'InstanceMirror on ${Error.safeToString(reflectee)}';
 
   // TODO(ahe): Remove this method from the API.