Implement type inference for symbol literals.

pkg/front_end/testcases/inference/symbol_literal.dart

Index: pkg/front_end/testcases/inference/symbol_literal.dart
diff --git a/pkg/front_end/testcases/inference/symbol_literal.dart b/pkg/front_end/testcases/inference/symbol_literal.dart
new file mode 100644
index 0000000000000000000000000000000000000000..7aeae82bdc0eb3421c3a6718d66c6d0732c2da3b
--- /dev/null
+++ b/pkg/front_end/testcases/inference/symbol_literal.dart
@@ -0,0 +1,12 @@
+// Copyright (c) 2017, 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.
+
+/*@testedFeatures=inference*/
+library test;
+
+void test() {
+  var /*@type=Symbol*/ x = #foo;
+}
+
+main() {}