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

chrome/browser/prefs/pref_notifier_impl_unittest.cc

Index: chrome/browser/prefs/pref_notifier_impl_unittest.cc
===================================================================
--- chrome/browser/prefs/pref_notifier_impl_unittest.cc	(revision 101967)
+++ chrome/browser/prefs/pref_notifier_impl_unittest.cc	(working copy)
@@ -104,13 +104,13 @@
   // Re-adding the same observer for the same pref doesn't change anything.
   // Skip this in debug mode, since it hits a DCHECK and death tests aren't
   // thread-safe.
-#if defined(NDEBUG)
+#if defined(NDEBUG) && !defined(DCHECK_ALWAYS_ON)
   notifier.AddPrefObserver(pref_name, &obs1_);
   ASSERT_EQ(1u, notifier.CountObserver(pref_name, &obs1_));
   ASSERT_EQ(0u, notifier.CountObserver(pref_name2, &obs1_));
   ASSERT_EQ(0u, notifier.CountObserver(pref_name, &obs2_));
   ASSERT_EQ(0u, notifier.CountObserver(pref_name2, &obs2_));
-#endif  // NDEBUG
+#endif
 
   // Ensure that we can add the same observer to a different pref.
   notifier.AddPrefObserver(pref_name2, &obs1_);