Fix VM crash when ClosureMirror.findInContext operates on a fake function.

tests/lib/mirrors/find_in_context_fake_function_test.dart

+// Copyright (c) 2013, 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.
+
+// Regression test: this used to crash the VM.
+
+library test.find_in_context_fake_function;
+
+import "dart:mirrors";
+import "package:expect/expect.dart";
+
+var topLevelField = 1;
+get topLevelGetter => 2;
+topLevelFunction() => 3;
+
+class FakeFunction1 {
+  var field = 4;
+  get getter => 5;
+  method() => 6;
+  static var staticField = 7;
+  static get staticGetter => 8;
+  staticFunction() => 9;
+  call(x) {
+    var local = x * 2;
+    return local;
+  }
+}
+
+class FakeFunction2 implements Function {
+  var field = 10;
+  get getter => 11;
+  method() => 12;
+  static var staticField = 13;
+  static get staticGetter => 14;
+  staticFunction() => 15;
+  noSuchMethod(msg) {
+    var local = msg.positionalArguments;
+    if (msg.memberName != #call) return super.noSuchMethod(msg);
+    return local.join('+');
+  }
+}
+
+doFindInContext(cm, name, value) {
+  Expect.equals(value,
+                cm.findInContext(name).reflectee);
+}
+dontFindInContext(cm, name) {
+  Expect.isNull(cm.findInContext(name));
+}
+
+main() {
+  ClosureMirror cm = reflect(new FakeFunction1());
+  dontFindInContext(cm, #local);
+  dontFindInContext(cm, const Symbol('this'));
+  dontFindInContext(cm, #field);
+  dontFindInContext(cm, #getter);
+  dontFindInContext(cm, #method);
+  dontFindInContext(cm, #staticField);
+  dontFindInContext(cm, #staticGetter);
+  dontFindInContext(cm, #staticFunction);
+  dontFindInContext(cm, #topLevelField);
+  dontFindInContext(cm, #topLevelGetter);
+  dontFindInContext(cm, #topLevelFunction);
+
+  cm = reflect(new FakeFunction2());
+  dontFindInContext(cm, #local);
+  dontFindInContext(cm, const Symbol('this'));
+  dontFindInContext(cm, #field);
+  dontFindInContext(cm, #getter);
+  dontFindInContext(cm, #method);
+  dontFindInContext(cm, #staticField);
+  dontFindInContext(cm, #staticGetter);
+  dontFindInContext(cm, #staticFunction);
+  dontFindInContext(cm, #topLevelField);
+  dontFindInContext(cm, #topLevelGetter);
+  dontFindInContext(cm, #topLevelFunction);
+}