Make x64 to use the RecordWrite stub. This is a step towards getting

src/x64/assembler-x64.h

Index: src/x64/assembler-x64.h
===================================================================
--- src/x64/assembler-x64.h	(revision 8207)
+++ src/x64/assembler-x64.h	(working copy)
@@ -1374,6 +1374,18 @@
 
   int pc_offset() const { return static_cast<int>(pc_ - buffer_); }
 
+  // Used for patching the code stream while it is being emitted.
+  inline byte get_opcode(int offset) {
+    ASSERT(offset < 0);
+    ASSERT(pc_ + offset >= buffer_);
+    return pc_[offset];
+  }
+  inline void set_opcode(int offset, byte opcode) {
+    ASSERT(offset < 0);
+    ASSERT(pc_ + offset >= buffer_);
+    pc_[offset] = opcode;
+  }
+
   PositionsRecorder* positions_recorder() { return &positions_recorder_; }
 
   // Check if there is less than kGap bytes available in the buffer.