Document the fact that SendPort.send() dispatches messages immediately.

sdk/lib/isolate/isolate.dart

Index: sdk/lib/isolate/isolate.dart
diff --git a/sdk/lib/isolate/isolate.dart b/sdk/lib/isolate/isolate.dart
index 8c2b86e18b024b381f38da6f75348dddbf804484..4d0b13a8d8977ccaf9eccca4b5d1021c60ac0037 100644
--- a/sdk/lib/isolate/isolate.dart
+++ b/sdk/lib/isolate/isolate.dart
@@ -485,6 +485,9 @@ abstract class SendPort implements Capability {
    * is also possible to send object instances (which would be copied in the
    * process). This is currently only supported by the dartvm.  For now, the
    * dart2js compiler only supports the restricted messages described above.
+   *
+   * The send is immediate--it is not necessary to yield control to the event
+   * loop, provided that the receiver is running in a parallel isolate.

[Lasse Reichstein Nielsen, 2015/08/31 19:45:20]

I don't think we use the term "parallel isolate" anywhere else.
Maybe just "in another isolate".
It's still a little vague - it's not saying what wouldn't work if it wasn't the
way it is, or why yielding to the event loop is relevant. 

Maybe instead say:

The send happens immediately and doesn't block. The corresponding receive port
can receive the message as soon as its isolate's event loop is ready to deliver
it, independently of what the sending isolate is doing.

Is that too wordy?

[Paul Berry, 2015/08/31 19:48:53]

Works for me.  PTAL.

    */
   void send(var message);