Make VM service id handling JSON-RPC 2 compliant.

runtime/vm/service_test.cc

Index: runtime/vm/service_test.cc
diff --git a/runtime/vm/service_test.cc b/runtime/vm/service_test.cc
index bbcd2a4f56af111198c91342982eb23e6456595b..5df9f0b50322cc96632924748beec92a44282712 100644
--- a/runtime/vm/service_test.cc
+++ b/runtime/vm/service_test.cc
@@ -530,15 +530,15 @@ TEST_CASE(Service_EmbedderRootHandler) {
 
 
   Array& service_msg = Array::Handle();
-  service_msg = Eval(lib, "[0, port, '0', 'alpha', [], []]");
+  service_msg = Eval(lib, "[0, port, '\"', 'alpha', [], []]");
   Service::HandleRootMessage(service_msg);
   handler.HandleNextMessage();
-  EXPECT_STREQ("{\"jsonrpc\":\"2.0\", \"result\":alpha, \"id\":\"0\"}",
+  EXPECT_STREQ("{\"jsonrpc\":\"2.0\", \"result\":alpha, \"id\":\"\\\"\"}",
                handler.msg());
-  service_msg = Eval(lib, "[0, port, '0', 'beta', [], []]");
+  service_msg = Eval(lib, "[0, port, 1, 'beta', [], []]");
   Service::HandleRootMessage(service_msg);
   handler.HandleNextMessage();
-  EXPECT_STREQ("{\"jsonrpc\":\"2.0\", \"result\":beta, \"id\":\"0\"}",
+  EXPECT_STREQ("{\"jsonrpc\":\"2.0\", \"result\":beta, \"id\":1}",
                handler.msg());
 }