Provide a counter for thrown JavaScript errors per context

src/contexts.cc

Index: src/contexts.cc
diff --git a/src/contexts.cc b/src/contexts.cc
index a18f181bef8ccb3e0ca80d43dc5a1f3107105d73..b599971ab979a2d50f50c8c026789f4f508ccdca 100644
--- a/src/contexts.cc
+++ b/src/contexts.cc
@@ -589,5 +589,18 @@ bool Context::IsBootstrappingOrGlobalObject(Isolate* isolate, Object* object) {
 }
 #endif
 
+
+void Context::IncrementErrorsThrown() {
+  DCHECK(IsNativeContext());
+
+  int previous_value = Smi::cast(errors_thrown())->value();

[Yang, 2015/11/02 05:48:57]

this cast would be unnecessary if the type of this field is defined as Smi.

[Michael Hablich, 2015/11/04 10:58:07]

Done.

+  set_errors_thrown(Smi::FromInt(previous_value+1));
+}
+
+
+int Context::GetErrorsThrown() {
+  return Smi::cast(errors_thrown())->value();
+}
+
 }  // namespace internal
 }  // namespace v8