Use a class field instead of global FLAG_debug_code in assember and

src/x64/assembler-x64.cc

Index: src/x64/assembler-x64.cc
diff --git a/src/x64/assembler-x64.cc b/src/x64/assembler-x64.cc
index f879ae7c2272efa1410b9ed38141d503fc4f9bf1..7eaac91d1e8ac46accfad751b034b8bbe70aadf9 100644
--- a/src/x64/assembler-x64.cc
+++ b/src/x64/assembler-x64.cc
@@ -338,7 +338,9 @@ static void InitCoverageLog();
 byte* Assembler::spare_buffer_ = NULL;
 
 Assembler::Assembler(void* buffer, int buffer_size)
-    : code_targets_(100), positions_recorder_(this) {
+    : code_targets_(100),
+      positions_recorder_(this),
+      emit_debug_code_(FLAG_debug_code) {
   if (buffer == NULL) {
     // Do our own buffer management.
     if (buffer_size <= kMinimalBufferSize) {
@@ -3114,7 +3116,7 @@ void Assembler::RecordRelocInfo(RelocInfo::Mode rmode, intptr_t data) {
       Serializer::TooLateToEnableNow();
     }
 #endif
-    if (!Serializer::enabled() && !FLAG_debug_code) {
+    if (!Serializer::enabled() && !emit_debug_code()) {
       return;
     }
   }