Add tool to visualize machine code/lithium.

src/hydrogen-instructions.h

Index: src/hydrogen-instructions.h
diff --git a/src/hydrogen-instructions.h b/src/hydrogen-instructions.h
index bdeec0c35dce4ee47c31163bf58232241d0721e1..68e8b22c854189de83f5070039d2ea35af8d72d2 100644
--- a/src/hydrogen-instructions.h
+++ b/src/hydrogen-instructions.h
@@ -638,6 +638,8 @@ class HValue : public ZoneObject {
         flags_(0) {}
   virtual ~HValue() {}
 
+  virtual int position() const { return RelocInfo::kNoPosition; }
+
   HBasicBlock* block() const { return block_; }
   void SetBlock(HBasicBlock* block);
   int LoopWeight() const;
@@ -1114,7 +1116,7 @@ class HInstruction : public HValue {
   void InsertAfter(HInstruction* previous);
 
   // The position is a write-once variable.
-  int position() const { return position_; }
+  virtual int position() const V8_OVERRIDE { return position_; }
   bool has_position() const { return position_ != RelocInfo::kNoPosition; }
   void set_position(int position) {
     ASSERT(!has_position());
@@ -3147,6 +3149,8 @@ class HPhi V8_FINAL : public HValue {
   bool IsReceiver() const { return merged_index_ == 0; }
   bool HasMergedIndex() const { return merged_index_ != kInvalidMergedIndex; }
 
+  virtual int position() const V8_OVERRIDE;
+
   int merged_index() const { return merged_index_; }
 
   InductionVariableData* induction_variable_data() {