Add a gyp flag to enable dcheck by default in release without

chrome/browser/prefs/incognito_mode_prefs_unittest.cc

 // Copyright (c) 2011 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.
 
 #include "chrome/browser/prefs/incognito_mode_prefs.h"
 
 #include "chrome/common/pref_names.h"
 #include "chrome/test/base/testing_pref_service.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
@@ skipping 40 matching lines @@
                      Value::CreateIntegerValue(IncognitoModePrefs::FORCED));
   EXPECT_EQ(IncognitoModePrefs::FORCED,
             IncognitoModePrefs::GetAvailability(&prefs_));
 }
 
 typedef IncognitoModePrefsTest IncognitoModePrefsDeathTest;
 
 TEST_F(IncognitoModePrefsDeathTest, GetAvailabilityBadValue) {
   prefs_.SetUserPref(prefs::kIncognitoModeAvailability,
                      Value::CreateIntegerValue(-1));
+#if defined(NDEBUG) && defined(DCHECK_ALWAYS_ON)
+  EXPECT_DEATH({
+    IncognitoModePrefs::Availability availability =
+        IncognitoModePrefs::GetAvailability(&prefs_);
+    EXPECT_EQ(IncognitoModePrefs::ENABLED, availability);
+  }, "");
+#else
   EXPECT_DEBUG_DEATH({
     IncognitoModePrefs::Availability availability =
         IncognitoModePrefs::GetAvailability(&prefs_);
     EXPECT_EQ(IncognitoModePrefs::ENABLED, availability);
   }, "");
+#endif
 }