rewrite_to_chrome_style: Handle non-method overloaded operators

tools/clang/rewrite_to_chrome_style/tests/operators-original.cc

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+namespace blink {
+
+struct Op {
+  bool operator==(const Op&) { return true; }
+};
+
+struct Op2 {};
+
+inline bool operator==(const Op2&, const Op2) {
+  return true;
+}
+
+}  // namespace
+
+void G() {
+  blink::Op a, b;
+  bool c = a == b;
+
+  blink::Op2 a2, b2;
+  bool c2 = a2 == b2;
+}