Add explicit class checks: LoadVMField.

runtime/vm/intermediate_language.h

Index: runtime/vm/intermediate_language.h
===================================================================
--- runtime/vm/intermediate_language.h	(revision 11587)
+++ runtime/vm/intermediate_language.h	(working copy)
@@ -1374,8 +1374,7 @@
                   const AbstractType& type)
       : offset_in_bytes_(offset_in_bytes),
         type_(type),
-        result_cid_(kDynamicCid),
-        original_(NULL) {
+        result_cid_(kDynamicCid) {
     ASSERT(value != NULL);
     ASSERT(type.IsZoneHandle());  // May be null if field is not an instance.
     inputs_[0] = value;
@@ -1386,21 +1385,17 @@
   Value* value() const { return inputs_[0]; }
   intptr_t offset_in_bytes() const { return offset_in_bytes_; }
   const AbstractType& type() const { return type_; }
-  const InstanceCallComp* original() const { return original_; }
-  void set_original(InstanceCallComp* value) { original_ = value; }
   void set_result_cid(intptr_t value) { result_cid_ = value; }
 
   virtual void PrintOperandsTo(BufferFormatter* f) const;
 
-  virtual bool CanDeoptimize() const { return true; }
+  virtual bool CanDeoptimize() const { return false; }
   virtual intptr_t ResultCid() const { return result_cid_; }
 
  private:
   const intptr_t offset_in_bytes_;
   const AbstractType& type_;
   intptr_t result_cid_;
-  const InstanceCallComp* original_;  // For optimizations.
-  // If non-NULL, the instruction is valid only for the class ids listed.
 
   DISALLOW_COPY_AND_ASSIGN(LoadVMFieldComp);
 };