Provide a counter for thrown JavaScript errors per context

src/bootstrapper.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/bootstrapper.h"
 
 #include "src/accessors.h"
 #include "src/api-natives.h"
 #include "src/base/utils/random-number-generator.h"
 #include "src/code-stubs.h"
@@ skipping 355 matching lines @@
 static void SetObjectPrototype(Handle<JSObject> object, Handle<Object> proto) {
   // object.__proto__ = proto;
   Handle<Map> old_map = Handle<Map>(object->map());
   Handle<Map> new_map = Map::Copy(old_map, "SetObjectPrototype");
   Map::SetPrototype(new_map, proto, FAST_PROTOTYPE);
   JSObject::MigrateToMap(object, new_map);
 }
 
 
 void Bootstrapper::DetachGlobal(Handle<Context> env) {
+  env->GetIsolate()->counters()->errors_thrown_per_context()->AddSample(
+    env->GetErrorsThrown());
+
   Factory* factory = env->GetIsolate()->factory();
   Handle<JSGlobalProxy> global_proxy(JSGlobalProxy::cast(env->global_proxy()));
   global_proxy->set_native_context(*factory->null_value());
   SetObjectPrototype(global_proxy, factory->null_value());
   global_proxy->map()->SetConstructor(*factory->null_value());
   if (FLAG_track_detached_contexts) {
     env->GetIsolate()->AddDetachedContext(env);
   }
 }
 
@@ skipping 2934 matching lines @@
 }
 
 
 // Called when the top-level V8 mutex is destroyed.
 void Bootstrapper::FreeThreadResources() {
   DCHECK(!IsActive());
 }
 
 }  // namespace internal
 }  // namespace v8