Add a HBreak instruction for debugging

src/hydrogen-instructions.h

Index: src/hydrogen-instructions.h
diff --git a/src/hydrogen-instructions.h b/src/hydrogen-instructions.h
index 138587c43f72b45b9be5193682174eb37b6896be..5f84d64aa6e981cc6d26a091a1c40c5bbf8f8a95 100644
--- a/src/hydrogen-instructions.h
+++ b/src/hydrogen-instructions.h
@@ -103,6 +103,7 @@ class LChunkBuilder;
   V(CompareConstantEqAndBranch)                \
   V(Constant)                                  \
   V(Context)                                   \
+  V(DebugBreak)                                \
   V(DeclareGlobals)                            \
   V(DeleteProperty)                            \
   V(Deoptimize)                                \
@@ -1463,6 +1464,17 @@ class HSoftDeoptimize: public HTemplateInstruction<0> {
 };
 
 
+// Inserts an int3/stop break instruction for debugging purposes.
+class HDebugBreak: public HTemplateInstruction<0> {
+ public:
+  virtual Representation RequiredInputRepresentation(int index) {
+    return Representation::None();
+  }
+
+  DECLARE_CONCRETE_INSTRUCTION(DebugBreak)
+};
+
+
 class HDeoptimize: public HControlInstruction {
  public:
   HDeoptimize(int environment_length, Zone* zone)