2nd attempt at adding streamListen/streamCancel to the service protocol.

runtime/vm/service_event.cc

Index: runtime/vm/service_event.cc
diff --git a/runtime/vm/service_event.cc b/runtime/vm/service_event.cc
index 0583da4f7ccb8511378b8cc7fd3f42dad5da3a0c..2c6680df21b2c1cc862434a8154dd7ddf25bfa73 100644
--- a/runtime/vm/service_event.cc
+++ b/runtime/vm/service_event.cc
@@ -84,6 +84,8 @@ const char* ServiceEvent::EventTypeToCString(EventType type) {
       return "GC";  // TODO(koda): Change to GarbageCollected.
     case kInspect:
       return "Inspect";
+    case kIllegal:
+      return "Illegal";
     default:
       UNREACHABLE();
       return "Unknown";
@@ -91,6 +93,35 @@ const char* ServiceEvent::EventTypeToCString(EventType type) {
 }
 
 
+const char* ServiceEvent::stream_id() const {
+  switch (type()) {
+    case kIsolateStart:
+    case kIsolateExit:
+    case kIsolateUpdate:
+      return "Isolate";
+
+    case kPauseStart:
+    case kPauseExit:
+    case kPauseBreakpoint:
+    case kPauseInterrupted:
+    case kPauseException:
+    case kResume:
+    case kBreakpointAdded:
+    case kBreakpointResolved:
+    case kBreakpointRemoved:
+    case kInspect:
+      return "Debug";
+
+    case kGC:
+      return "GC";
+
+    default:
+      UNREACHABLE();
+      return NULL;
+  }
+}
+
+
 void ServiceEvent::PrintJSON(JSONStream* js) const {
   JSONObject jsobj(js);
   jsobj.AddProperty("type", "Event");