Provide a counter for thrown JavaScript errors per context

src/bootstrapper.cc

Index: src/bootstrapper.cc
diff --git a/src/bootstrapper.cc b/src/bootstrapper.cc
index 069a2c2e3400d7b0838e6990b87ebf00bc247893..9d2ae1b56c44aa82cb8b5cdf1f1ad0f3eaee105f 100644
--- a/src/bootstrapper.cc
+++ b/src/bootstrapper.cc
@@ -370,6 +370,9 @@ static void SetObjectPrototype(Handle<JSObject> object, Handle<Object> proto) {
 
 
 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());
@@ -3151,6 +3154,11 @@ Genesis::Genesis(Isolate* isolate,
     AddToWeakNativeContextList(*native_context());
     isolate->set_context(*native_context());
     isolate->counters()->contexts_created_by_snapshot()->Increment();
+
+    // Re-initialize the counter because it got incremented during snapshot
+    // creation.
+    isolate->native_context()->set_errors_thrown(Smi::FromInt(0));

[Yang, 2015/11/05 07:50:01]

Move this below please. Otherwise we would get wrong numbers if no snapshot was
present.

[Michael Hablich, 2015/11/05 13:23:11]

After an offline discussion I now get it why it should be down there. Thanks.
done.

+
 #if TRACE_MAPS
     if (FLAG_trace_maps) {
       Handle<JSFunction> object_fun = isolate->object_function();