Do not ignore side effects of a type test or type cast as expression, such

runtime/vm/object.cc

Index: runtime/vm/object.cc
===================================================================
--- runtime/vm/object.cc	(revision 35282)
+++ runtime/vm/object.cc	(working copy)
@@ -14201,7 +14201,8 @@
   if (bounded_type.IsSubtypeOf(upper_bound, bound_error)) {
     return true;
   }
-  if (bound_error->IsNull()) {
+  // Set bound_error if the caller is interested and if this is the first error.
+  if ((bound_error != NULL) && bound_error->IsNull()) {
     // Report the bound error only if both the bounded type and the upper bound
     // are instantiated. Otherwise, we cannot tell yet it is a bound error.
     if (bounded_type.IsInstantiated() && upper_bound.IsInstantiated()) {
@@ -14430,7 +14431,8 @@
                                                 bound_error,
                                                 trail);
   }
-  if (FLAG_enable_type_checks && bound_error->IsNull()) {
+  if (FLAG_enable_type_checks &&
+      (bound_error != NULL) && bound_error->IsNull()) {
     AbstractType& upper_bound = AbstractType::Handle(bound());
     ASSERT(!upper_bound.IsObjectType() && !upper_bound.IsDynamicType());
     const TypeParameter& type_param = TypeParameter::Handle(type_parameter());