Provide a counter for thrown JavaScript errors per context

src/contexts.h

Index: src/contexts.h
diff --git a/src/contexts.h b/src/contexts.h
index 3eec6b7f54afc9f4f94b079a6b36282fb533c2c0..4f0dfaf81f87db4a945906f06814fdfbae5b0e06 100644
--- a/src/contexts.h
+++ b/src/contexts.h
@@ -186,6 +186,7 @@ enum BindingFlags {
   V(DATA_VIEW_FUN_INDEX, JSFunction, data_view_fun)                            \
   V(ERROR_MESSAGE_FOR_CODE_GEN_FROM_STRINGS_INDEX, Object,                     \
     error_message_for_code_gen_from_strings)                                   \
+  V(EXCEPTION_THROWN_INDEX, Object, exceptions_thrown)                         \
   V(EXTRAS_EXPORTS_OBJECT_INDEX, JSObject, extras_binding_object)              \
   V(EXTRAS_UTILS_OBJECT_INDEX, JSObject, extras_utils_object)                  \
   V(FAST_ALIASED_ARGUMENTS_MAP_INDEX, Map, fast_aliased_arguments_map)         \
@@ -396,6 +397,9 @@ class Context: public FixedArray {
     THROWN_OBJECT_INDEX = MIN_CONTEXT_SLOTS,
   };
 
+  void IncrementExceptionsThrown();
+  int GetExceptionsThrown();
+
   // Direct slot access.
   inline JSFunction* closure();
   inline void set_closure(JSFunction* closure);