Define XxxStream.prototype.onread as an accessor in JavaScript sense (#…

…183)

Previously is was defined via soon-to-be-deprecated
`v8::ObjectTemplate::SetAccessor(..)` which used to call setter even
for property stores via stream object.

The replacement V8 Api `v8::ObjectTemplate::SetNativeDataProperty(..)`
defines a properly behaving data property and thus a store to a stream
object will not trigger the "onread" setter callback.

In order to preserve the desired behavior of storing the value in the
receiver's internal field the "onread" property should be defined as
a proper JavaScript accessor.
# Conflicts:
#	src/base_object-inl.h

src/base_object-inl.h

@@ -140,8 +140,8 @@ void BaseObject::InternalFieldGet(
 template <int Field, bool (v8::Value::*typecheck)() const>
 void BaseObject::InternalFieldSet(
     const v8::FunctionCallbackInfo<v8::Value>& args) {
-  v8::Local<v8::Value> value = args[0];
   // This could be e.g. value->IsFunction().
+  v8::Local<v8::Value> value = args[0];
   CHECK(((*value)->*typecheck)());
   args.This()->SetInternalField(Field, value);
 }