Add support for enabling DCHECKs in release mode

src/runtime/runtime-strings.cc

Index: src/runtime/runtime-strings.cc
diff --git a/src/runtime/runtime-strings.cc b/src/runtime/runtime-strings.cc
index df2210c635198410a939c26529a01948a3e5f6aa..aceceb409056c0e8468b5352a10ab5a16bbc8724 100644
--- a/src/runtime/runtime-strings.cc
+++ b/src/runtime/runtime-strings.cc
@@ -607,7 +607,7 @@ RUNTIME_FUNCTION(Runtime_StringBuilderJoin) {
   DisallowHeapAllocation no_gc;
 
   uc16* sink = answer->GetChars();
-#ifdef DEBUG
+#if DCHECK_IS_ON
   uc16* end = sink + length;
 #endif
 
@@ -978,7 +978,7 @@ static inline uintptr_t AsciiRangeMask(uintptr_t w, char m, char n) {
 }
 
 
-#ifdef DEBUG
+#if DCHECK_IS_ON
 static bool CheckFastAsciiConvert(char* dst, const char* src, int length,
                                   bool changed, bool is_to_lower) {
   bool expected_changed = false;
@@ -1001,7 +1001,7 @@ static bool CheckFastAsciiConvert(char* dst, const char* src, int length,
 template <class Converter>
 static bool FastAsciiConvert(char* dst, const char* src, int length,
                              bool* changed_out) {
-#ifdef DEBUG
+#if DCHECK_IS_ON
   char* saved_dst = dst;
   const char* saved_src = src;
 #endif