Have --print-metrics use stderr to work around issue with analyzer_cli

runtime/vm/metrics.cc

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/metrics.h"
 
 #include "vm/isolate.h"
 #include "vm/json_stream.h"
 #include "vm/native_entry.h"
 #include "vm/runtime_entry.h"
@@ skipping 288 matching lines @@
 #define VM_METRIC_INIT(type, variable, name, unit)                             \
   vm_metric_##variable##_.Init(name, NULL, Metric::unit);
   VM_METRIC_LIST(VM_METRIC_INIT);
 #undef VM_METRIC_INIT
 }
 
 void Metric::Cleanup() {
   if (FLAG_print_metrics) {
     // Create a zone to allocate temporary strings in.
     StackZone sz(Thread::Current());
-    OS::Print("Printing metrics for VM\n");
+    OS::PrintErr("Printing metrics for VM\n");
     Metric* current = Metric::vm_head();
     while (current != NULL) {
-      OS::Print("%s\n", current->ToString());
+      OS::PrintErr("%s\n", current->ToString());
       current = current->next();
     }
-    OS::Print("\n");
+    OS::PrintErr("\n");
   }
 }
 
 
 MaxMetric::MaxMetric()
     : Metric() {
   set_value(kMinInt64);
 }
 
 
@@ skipping 10 matching lines @@
 }
 
 
 void MinMetric::SetValue(int64_t new_value) {
   if (new_value < value()) {
     set_value(new_value);
   }
 }
 
 }  // namespace dart