Add write barrier helper for code patching and refactor stack check patching.

src/x64/lithium-codegen-x64.h

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 172 matching lines @@
                    int num_arguments,
                    LInstruction* instr) {
     const Runtime::Function* function = Runtime::FunctionForId(id);
     CallRuntime(function, num_arguments, instr);
   }
 
   void CallRuntimeFromDeferred(Runtime::FunctionId id,
                                int argc,
                                LInstruction* instr);
 
-
   // Generate a direct call to a known function.  Expects the function
-  // to be in edi.
+  // to be in rdi.
   void CallKnownFunction(Handle<JSFunction> function,
                          int arity,
                          LInstruction* instr,
                          CallKind call_kind);
 
   void LoadHeapObject(Register result, Handle<HeapObject> object);
 
   void RegisterLazyDeoptimization(LInstruction* instr,
                                   SafepointMode safepoint_mode,
                                   int argc);
@@ skipping 165 matching lines @@
   LCodeGen* codegen_;
   Label entry_;
   Label exit_;
   Label* external_exit_;
   int instruction_index_;
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_X64_LITHIUM_CODEGEN_X64_H_