Use a class field instead of global FLAG_debug_code in assember and

src/x64/assembler-x64.h

Index: src/x64/assembler-x64.h
diff --git a/src/x64/assembler-x64.h b/src/x64/assembler-x64.h
index 4360e1eda7adfe13e214dfcb4e84574f1feb72fb..9fcb95c96e805d5494dfd5c37582ade38e07bb5a 100644
--- a/src/x64/assembler-x64.h
+++ b/src/x64/assembler-x64.h
@@ -511,6 +511,9 @@ class Assembler : public Malloced {
   Assembler(void* buffer, int buffer_size);
   ~Assembler();
 
+  // Overrides the default provided by FLAG_debug_code.
+  void set_emit_debug_code(bool value) { emit_debug_code_ = value; }
+
   // GetCode emits any pending (non-emitted) code and fills the descriptor
   // desc. GetCode() is idempotent; it returns the same result if no other
   // Assembler functions are invoked in between GetCode() calls.
@@ -1350,6 +1353,9 @@ class Assembler : public Malloced {
   static const int kMaximalBufferSize = 512*MB;
   static const int kMinimalBufferSize = 4*KB;
 
+ protected:
+  bool emit_debug_code() const { return emit_debug_code_; }
+
  private:
   byte* addr_at(int pos)  { return buffer_ + pos; }
   byte byte_at(int pos)  { return buffer_[pos]; }
@@ -1555,6 +1561,9 @@ class Assembler : public Malloced {
   byte* last_pc_;
 
   PositionsRecorder positions_recorder_;
+
+  bool emit_debug_code_;
+
   friend class PositionsRecorder;
 };