Bug fixes for hot reload

runtime/vm/object_reload.cc

Index: runtime/vm/object_reload.cc
diff --git a/runtime/vm/object_reload.cc b/runtime/vm/object_reload.cc
index ba5098a05b62c66449661e430a21bd44d7834d95..f9c5ad9869e4fffd1c825f305413977bfb0a8bb2 100644
--- a/runtime/vm/object_reload.cc
+++ b/runtime/vm/object_reload.cc
@@ -444,13 +444,22 @@ bool Class::CanReload(const Class& replacement) const {
     const Array& replacement_fields =
         Array::Handle(replacement.OffsetToFieldMap());
 
-    // Check that we have the same number of fields.
+    // Check that the size of the instance is the same.
     if (fields.Length() != replacement_fields.Length()) {
       IRC->ReportError(String::Handle(String::NewFormatted(
           "Number of instance fields changed in %s", ToCString())));
       return false;
     }
 
+    // Check that we have the same next field offset. This check is not
+    // redundant with the one above because the instance OffsetToFieldMap
+    // array length is based on the instance size (which may be aligned up).
+    if (next_field_offset() != replacement.next_field_offset()) {
+      IRC->ReportError(String::Handle(String::NewFormatted(
+          "Number of instance fields changed in %s", ToCString())));
+      return false;
+    }
+
     if (NumTypeArguments() != replacement.NumTypeArguments()) {
       IRC->ReportError(String::Handle(String::NewFormatted(
           "Number of type arguments changed in %s", ToCString())));
@@ -483,7 +492,8 @@ bool Class::CanReload(const Class& replacement) const {
   } else if (is_prefinalized()) {
     if (!replacement.is_prefinalized()) {
       IRC->ReportError(String::Handle(String::NewFormatted(
-          "Original class ('%s') is prefinalized and replacement class ('%s')",
+          "Original class ('%s') is prefinalized and replacement class "
+          "('%s') is not ",
           ToCString(), replacement.ToCString())));
       return false;
     }