Handle HCheckInstanceType and HIsStringAndBranch in check elimination.

src/hydrogen-instructions.h

Index: src/hydrogen-instructions.h
diff --git a/src/hydrogen-instructions.h b/src/hydrogen-instructions.h
index 908faa8011d90142295ee522345fbaf69c0ac181..90bff265d13aa3fb5e54867d67de810553c1998d 100644
--- a/src/hydrogen-instructions.h
+++ b/src/hydrogen-instructions.h
@@ -2907,6 +2907,8 @@ class HCheckInstanceType V8_FINAL : public HUnaryOperation {
   void GetCheckInterval(InstanceType* first, InstanceType* last);
   void GetCheckMaskAndTag(uint8_t* mask, uint8_t* tag);
 
+  Check check() const { return check_; }
+
   DECLARE_CONCRETE_INSTRUCTION(CheckInstanceType)
 
  protected:
@@ -4423,6 +4425,12 @@ class HIsStringAndBranch V8_FINAL : public HUnaryControlInstruction {
 
   virtual bool KnownSuccessorBlock(HBasicBlock** block) V8_OVERRIDE;
 
+  static const int kNoKnownSuccessorIndex = -1;
+  int known_successor_index() const { return known_successor_index_; }
+  void set_known_successor_index(int known_successor_index) {
+    known_successor_index_ = known_successor_index;
+  }
+
   DECLARE_CONCRETE_INSTRUCTION(IsStringAndBranch)
 
  protected:
@@ -4432,7 +4440,10 @@ class HIsStringAndBranch V8_FINAL : public HUnaryControlInstruction {
   HIsStringAndBranch(HValue* value,
                      HBasicBlock* true_target = NULL,
                      HBasicBlock* false_target = NULL)
-    : HUnaryControlInstruction(value, true_target, false_target) {}
+    : HUnaryControlInstruction(value, true_target, false_target),
+      known_successor_index_(kNoKnownSuccessorIndex) { }
+
+  int known_successor_index_;
 };