Add a HBreak instruction for debugging

src/x64/lithium-x64.h

Index: src/x64/lithium-x64.h
diff --git a/src/x64/lithium-x64.h b/src/x64/lithium-x64.h
index d6c3d9580e72842c9384c5f09103c4efaadd275c..9ad7268f9bef4e2959159bfb03418b18a26df0a9 100644
--- a/src/x64/lithium-x64.h
+++ b/src/x64/lithium-x64.h
@@ -60,6 +60,7 @@ class LCodeGen;
   V(BitNotI)                                    \
   V(BoundsCheck)                                \
   V(Branch)                                     \
+  V(Break)                                      \
   V(CallConstantFunction)                       \
   V(CallFunction)                               \
   V(CallGlobal)                                 \
@@ -1172,6 +1173,12 @@ class LBranch: public LControlInstruction<1, 0> {
 };
 
 
+class LBreak: public LTemplateInstruction<0, 0, 0> {
+ public:
+  DECLARE_CONCRETE_INSTRUCTION(Break, "break")
+};
+
+
 class LCmpMapAndBranch: public LTemplateInstruction<0, 1, 0> {
  public:
   explicit LCmpMapAndBranch(LOperand* value) {