Fix asserts in StackFrameIterator which were effectively disabled

runtime/lib/errors.cc

Index: runtime/lib/errors.cc
diff --git a/runtime/lib/errors.cc b/runtime/lib/errors.cc
index d10df392e2d4e5aa0a3cf11a260fea310d1bcd3c..c60e746bd7a04e94ae2d527479a409d4b23989ac 100644
--- a/runtime/lib/errors.cc
+++ b/runtime/lib/errors.cc
@@ -75,7 +75,7 @@ DEFINE_NATIVE_ENTRY(AssertionError_throwNew, 3) {
   const Instance& message = Instance::CheckedHandle(arguments->NativeArgAt(2));
   const Array& args = Array::Handle(Array::New(5));
 
-  DartFrameIterator iterator;
+  DartFrameIterator iterator(thread, false);

[Vyacheslav Egorov (Google), 2017/05/01 15:54:38]

I suggest that this false needs a name. 

thread, kNoCrossThreadIteration
thread, kAllowCrossThreadIteration

reads better than

thread, false
thread, true

[kustermann, 2017/05/02 07:11:18]

Made both bools an enum

   iterator.NextFrame();  // Skip native call.
   const Script& script = Script::Handle(FindScript(&iterator));
 
@@ -139,7 +139,7 @@ DEFINE_NATIVE_ENTRY(FallThroughError_throwNew, 1) {
   const Array& args = Array::Handle(Array::New(2));
 
   // Initialize 'url' and 'line' arguments.
-  DartFrameIterator iterator;
+  DartFrameIterator iterator(thread, false);
   iterator.NextFrame();  // Skip native call.
   const Script& script = Script::Handle(Exceptions::GetCallerScript(&iterator));
   args.SetAt(0, String::Handle(script.url()));
@@ -165,7 +165,7 @@ DEFINE_NATIVE_ENTRY(AbstractClassInstantiationError_throwNew, 2) {
   const Array& args = Array::Handle(Array::New(3));
 
   // Initialize 'className', 'url' and 'line' arguments.
-  DartFrameIterator iterator;
+  DartFrameIterator iterator(thread, false);
   iterator.NextFrame();  // Skip native call.
   const Script& script = Script::Handle(Exceptions::GetCallerScript(&iterator));
   args.SetAt(0, class_name);