Provide a counter for thrown JavaScript errors per context

src/factory.cc

Index: src/factory.cc
diff --git a/src/factory.cc b/src/factory.cc
index f475efcc7725c72a9179a1b580baae0e44116ecb..da7ba35c6e4dc23828509eee98f34a8f9a4f8389 100644
--- a/src/factory.cc
+++ b/src/factory.cc
@@ -726,6 +726,7 @@ Handle<Context> Factory::NewNativeContext() {
   array->set_map_no_write_barrier(*native_context_map());
   Handle<Context> context = Handle<Context>::cast(array);
   context->set_js_array_maps(*undefined_value());
+  context->set_exceptions_thrown(Smi::FromInt(0));
   DCHECK(context->IsNativeContext());
   return context;
 }
@@ -1159,6 +1160,7 @@ Handle<Object> Factory::NewError(Handle<JSFunction> constructor,
   Handle<Object> Factory::New##NAME(MessageTemplate::Template template_index, \
                                     Handle<Object> arg0, Handle<Object> arg1, \
                                     Handle<Object> arg2) {                    \
+    isolate()->native_context()->IncrementExceptionsThrown();                 \

[jochen (gone - plz use gerrit), 2015/10/30 12:13:38]

this looks wrong. It's not uncommon to do

var a = new Error().stack;

to capture e.g. the creation site of an object

[Yang, 2015/10/30 13:01:02]

As discussed offline, I suggested to do it in %FormatMessageString.

[Michael Hablich, 2015/10/30 15:55:03]

I moved the call to %FormatMessageString. During the build %FormatMessageString
is run once and the result is stored. This resulted in the weird behavior I
observed before. Initializing the counter with -1 fixes this.

     return NewError(isolate()->name##_function(), template_index, arg0, arg1, \
                     arg2);                                                    \
   }