[vm, gardening] Move --trace-service output to stderr.

runtime/vm/json_stream.cc

Index: runtime/vm/json_stream.cc
diff --git a/runtime/vm/json_stream.cc b/runtime/vm/json_stream.cc
index 8700dc787a443571b18305e603edd3d360ffe996..4c229c9f368d664885e36fcf46e933faa4f893c9 100644
--- a/runtime/vm/json_stream.cc
+++ b/runtime/vm/json_stream.cc
@@ -124,8 +124,8 @@ void JSONStream::Setup(Zone* zone,
     ASSERT(isolate != NULL);
     const char* isolate_name = isolate->name();
     setup_time_micros_ = OS::GetCurrentTimeMicros();
-    OS::Print("[+%" Pd64 "ms] Isolate %s processing service request %s\n",
-              Dart::UptimeMillis(), isolate_name, method_);
+    OS::PrintErr("[+%" Pd64 "ms] Isolate %s processing service request %s\n",
+                 Dart::UptimeMillis(), isolate_name, method_);
   }
   buffer_.Printf("{\"jsonrpc\":\"2.0\", \"result\":");
 }
@@ -282,15 +282,15 @@ void JSONStream::PostReply() {
     const char* isolate_name = isolate->name();
     int64_t total_time = OS::GetCurrentTimeMicros() - setup_time_micros_;
     if (result) {
-      OS::Print("[+%" Pd64
-                "ms] Isolate %s processed service request %s "
-                "(%" Pd64 "us)\n",
-                Dart::UptimeMillis(), isolate_name, method_, total_time);
+      OS::PrintErr("[+%" Pd64
+                   "ms] Isolate %s processed service request %s "
+                   "(%" Pd64 "us)\n",
+                   Dart::UptimeMillis(), isolate_name, method_, total_time);
     } else {
-      OS::Print("[+%" Pd64
-                "ms] Isolate %s processed service request %s "
-                "(%" Pd64 "us) FAILED\n",
-                Dart::UptimeMillis(), isolate_name, method_, total_time);
+      OS::PrintErr("[+%" Pd64
+                   "ms] Isolate %s processed service request %s "
+                   "(%" Pd64 "us) FAILED\n",
+                   Dart::UptimeMillis(), isolate_name, method_, total_time);
     }
   }
 }