Add code comments to deferred code objects to make debugging easier.

src/arm/lithium-codegen-arm.h

Index: src/arm/lithium-codegen-arm.h
===================================================================
--- src/arm/lithium-codegen-arm.h	(revision 9418)
+++ src/arm/lithium-codegen-arm.h	(working copy)
@@ -376,16 +376,20 @@
 class LDeferredCode: public ZoneObject {
  public:
   explicit LDeferredCode(LCodeGen* codegen)
-      : codegen_(codegen), external_exit_(NULL) {
+      : codegen_(codegen),
+        external_exit_(NULL),
+        instruction_index_(codegen->current_instruction_) {
     codegen->AddDeferredCode(this);
   }
 
   virtual ~LDeferredCode() { }
   virtual void Generate() = 0;
+  virtual LInstruction* instr() = 0;
 
   void SetExit(Label *exit) { external_exit_ = exit; }
   Label* entry() { return &entry_; }
   Label* exit() { return external_exit_ != NULL ? external_exit_ : &exit_; }
+  int instruction_index() const { return instruction_index_; }
 
  protected:
   LCodeGen* codegen() const { return codegen_; }
@@ -396,6 +400,7 @@
   Label entry_;
   Label exit_;
   Label* external_exit_;
+  int instruction_index_;
 };
 
 } }  // namespace v8::internal