Optimize the message queue for many active ports with few messages.

runtime/vm/dart_entry.cc

Index: runtime/vm/dart_entry.cc
diff --git a/runtime/vm/dart_entry.cc b/runtime/vm/dart_entry.cc
index 493af6ccdd6168447edc24eb8844dc32d6c39f3f..db4ecb02a1e2bfab9289f9a1f6bdf566404198bc 100644
--- a/runtime/vm/dart_entry.cc
+++ b/runtime/vm/dart_entry.cc
@@ -283,7 +283,33 @@ RawObject* DartLibraryCalls::Equals(const Instance& left,
 }
 
 
-RawObject* DartLibraryCalls::HandleMessage(Dart_Port dest_port_id,
+RawObject* DartLibraryCalls::LookupReceivePort(Dart_Port port_id) {
+  Library& isolate_lib = Library::Handle(Library::IsolateLibrary());
+  ASSERT(!isolate_lib.IsNull());
+  const String& public_class_name =
+      String::Handle(Symbols::New("_ReceivePortImpl"));
+  const String& class_name =
+      String::Handle(isolate_lib.PrivateName(public_class_name));
+  const String& function_name =
+      String::Handle(Symbols::New("_lookupReceivePort"));
+  const int kNumArguments = 1;
+  const Array& kNoArgumentNames = Array::Handle();
+  const Function& function = Function::Handle(
+      Resolver::ResolveStatic(isolate_lib,
+                              class_name,
+                              function_name,
+                              kNumArguments,
+                              kNoArgumentNames,
+                              Resolver::kIsQualified));
+  GrowableArray<const Object*> arguments(kNumArguments);
+  arguments.Add(&Integer::Handle(Integer::New(port_id)));
+  const Object& result = Object::Handle(
+      DartEntry::InvokeStatic(function, arguments, kNoArgumentNames));
+  return result.raw();
+}
+
+
+RawObject* DartLibraryCalls::HandleMessage(const Object& receive_port,
                                            Dart_Port reply_port_id,
                                            const Instance& message) {
   Library& isolate_lib = Library::Handle(Library::IsolateLibrary());
@@ -304,7 +330,7 @@ RawObject* DartLibraryCalls::HandleMessage(Dart_Port dest_port_id,
                               kNoArgumentNames,
                               Resolver::kIsQualified));
   GrowableArray<const Object*> arguments(kNumArguments);
-  arguments.Add(&Integer::Handle(Integer::New(dest_port_id)));
+  arguments.Add(&receive_port);
   arguments.Add(&Integer::Handle(Integer::New(reply_port_id)));
   arguments.Add(&message);
   const Object& result = Object::Handle(