Fix bug with guarded fields and deserialization.

runtime/vm/object.h

Index: runtime/vm/object.h
===================================================================
--- runtime/vm/object.h	(revision 29540)
+++ runtime/vm/object.h	(working copy)
@@ -863,6 +863,10 @@
   RawArray* fields() const { return raw_ptr()->fields_; }
   void SetFields(const Array& value) const;
 
+  // Returns an array of all fields of this class and its superclasses indexed
+  // by offset in words.
+  RawArray* OffsetToFieldMap() const;
+
   // Returns true if non-static fields are defined.
   bool HasInstanceFields() const;
 
@@ -2124,13 +2128,9 @@
     return OFFSET_OF(RawField, is_nullable_);
   }
 
-  // Update guarded class id and nullability of the field to reflect assignment
-  // of the value with the given class id to this field. May trigger
-  // deoptimization of dependent code.
-  void UpdateCid(intptr_t cid) const;
-  // Update guarded class length of the field to reflect assignment of the
-  // value with the given length. May trigger deoptimization of dependent code.
-  void UpdateLength(intptr_t length) const;
+  // Update guarded cid and guarded length for this field. May trigger
+  // deoptimization of dependent optimized code.
+  bool UpdateGuardedCidAndLength(const Object& value) const;
 
   // Return the list of optimized code objects that were optimized under
   // assumptions about guarded class id and nullability of this field.
@@ -2169,6 +2169,16 @@
   class FinalBit : public BitField<bool, kFinalBit, 1> {};
   class HasInitializerBit : public BitField<bool, kHasInitializerBit, 1> {};
 
+  // Update guarded class id and nullability of the field to reflect assignment
+  // of the value with the given class id to this field. Returns true, if
+  // deoptimization of dependent code is required.
+  bool UpdateCid(intptr_t cid) const;
+
+  // Update guarded class length of the field to reflect assignment of the
+  // value with the given length. Returns true if deoptimization of dependent
+  // code is required.
+  bool UpdateLength(intptr_t length) const;
+
   void set_name(const String& value) const;
   void set_is_static(bool is_static) const {
     set_kind_bits(StaticBit::update(is_static, raw_ptr()->kind_bits_));
@@ -3828,6 +3838,7 @@
   }
 
   void SetField(const Field& field, const Object& value) const {
+    field.UpdateGuardedCidAndLength(value);
     StorePointer(FieldAddr(field), value.raw());
   }