Add support for enabling DCHECKs in release mode

src/flag-definitions.h

Index: src/flag-definitions.h
diff --git a/src/flag-definitions.h b/src/flag-definitions.h
index 4d9b2b296a36dc3d5439ce9c9e7855c01ceff67f..3ce233dd28152760055856d795b27addb1ed193c 100644
--- a/src/flag-definitions.h
+++ b/src/flag-definitions.h
@@ -756,6 +756,12 @@ DEFINE_BOOL(stress_compaction, false,
             "stress the GC compactor to flush out bugs (implies "
             "--force_marking_deque_overflows)")
 
+// checks.cc
+#ifdef ENABLE_SLOW_DCHECKS
+DEFINE_BOOL(enable_slow_asserts, false,
+            "enable asserts that are slow to execute")
+#endif
+
 //
 // Debug only flags
 //
@@ -766,12 +772,6 @@ DEFINE_BOOL(stress_compaction, false,
 #define FLAG FLAG_READONLY
 #endif
 
-// checks.cc
-#ifdef ENABLE_SLOW_DCHECKS
-DEFINE_BOOL(enable_slow_asserts, false,
-            "enable asserts that are slow to execute")
-#endif
-
 // codegen-ia32.cc / codegen-arm.cc / macro-assembler-*.cc
 DEFINE_BOOL(print_source, false, "pretty print source code")
 DEFINE_BOOL(print_builtin_source, false,