Add optional message argument to assert statements in the VM.

runtime/vm/code_generator.cc

Index: runtime/vm/code_generator.cc
diff --git a/runtime/vm/code_generator.cc b/runtime/vm/code_generator.cc
index d0c073238644a64986b82c932bb0a987eb229d96..495277caf5934a618c853e0374220e4e1efcfaa2 100644
--- a/runtime/vm/code_generator.cc
+++ b/runtime/vm/code_generator.cc
@@ -585,7 +585,7 @@ DEFINE_RUNTIME_ENTRY(NonBoolTypeError, 1) {
       Instance::CheckedHandle(zone, arguments.ArgAt(0));
 
   if (src_instance.IsNull()) {
-    const Array& args = Array::Handle(zone, Array::New(4));
+    const Array& args = Array::Handle(zone, Array::New(5));
     args.SetAt(
         0, String::Handle(
                zone,
@@ -596,6 +596,7 @@ DEFINE_RUNTIME_ENTRY(NonBoolTypeError, 1) {
     args.SetAt(1, String::Handle(zone, String::null()));
     args.SetAt(2, Smi::Handle(zone, Smi::New(0)));
     args.SetAt(3, Smi::Handle(zone, Smi::New(0)));
+    args.SetAt(4, String::Handle(zone, String::null()));
 
     Exceptions::ThrowByType(Exceptions::kAssertion, args);
     UNREACHABLE();