Re-enable the clang check for enum constants.

tools/clang/plugins/tests/enum_last_value_from_c.c

+// Copyright 2014 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.
+
+// We warn when xxxLAST constants aren't last.
+enum BadOne {
+  kBadOneInvalid = -1,
+  kBadOneRed,
+  kBadOneGreen,
+  kBadOneBlue,
+  kBadOneLast = kBadOneGreen
+};
+
+// We don't handle this case when called from C due to sign mismatch issues.
+// No matter; we're not looking for this issue outside of C++.
+enum FailOne {
+  FAIL_ONE_INVALID,
+  FAIL_ONE_RED,
+  FAIL_ONE_GREEN,
+  FAIL_ONE_BLUE = 0xfffffffc,
+  FAIL_ONE_LAST = FAIL_ONE_GREEN
+};
+
+// We dont warn when xxxLAST constants are last.

[Nico, 2014/03/28 03:31:51]

don't

+enum GoodOne {
+  kGoodOneInvalid = -1,
+  kGoodOneRed,
+  kGoodOneGreen,
+  kGoodOneBlue,
+  kGoodOneLast = kGoodOneBlue
+};
+
+// We dont warn when xxx_LAST constants are last.

[Nico, 2014/03/28 03:31:51]

don't

+enum GoodTwo {
+  GOOD_TWO_INVALID,
+  GOOD_TWO_RED,
+  GOOD_TWO_GREEN,
+  GOOD_TWO_BLUE = 0xfffffffc,
+  GOOD_TWO_LAST = GOOD_TWO_BLUE
+};