Add the streamListen and streamCancel rpcs to the vm service.

runtime/vm/json_stream.h

Index: runtime/vm/json_stream.h
diff --git a/runtime/vm/json_stream.h b/runtime/vm/json_stream.h
index 3c3bc9c1d3b83244f19c7a3f17a577179f7cb4b3..f500a3754ac2d4e33cb33cf1a1ca0f9e8c7bc237 100644
--- a/runtime/vm/json_stream.h
+++ b/runtime/vm/json_stream.h
@@ -34,11 +34,16 @@ enum JSONRpcErrorCode {
   kInvalidParams  = -32602,
   kInternalError  = -32603,
 
-  kVMMustBePaused    = 100,
-  kNoBreakAtLine     = 101,
-  kNoBreakAtFunction = 102,
+  // These must be kept in sync with vm/service/vmservice.dart.
+  kInvalidStream           = 100,
+  kStreamAlreadySubscribed = 101,
+  kStreamNotSubscribed     = 102,
 
-  kProfilingDisabled = 200,
+  kVMMustBePaused    = 200,
+  kNoBreakAtLine     = 201,
+  kNoBreakAtFunction = 202,
+
+  kProfilingDisabled = 300,
 };