Specify kSmiCid as result of get string or array length operation.

runtime/vm/intermediate_language.h

Index: runtime/vm/intermediate_language.h
===================================================================
--- runtime/vm/intermediate_language.h	(revision 11232)
+++ runtime/vm/intermediate_language.h	(working copy)
@@ -1398,6 +1398,7 @@
                   const AbstractType& type)
       : offset_in_bytes_(offset_in_bytes),
         type_(type),
+        result_cid_(kDynamicCid),
         original_(NULL) {
     ASSERT(value != NULL);
     ASSERT(type.IsZoneHandle());  // May be null if field is not an instance.
@@ -1411,14 +1412,17 @@
   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 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.