Remove signature classes from the VM.

runtime/vm/log.cc

 // Copyright (c) 2015, 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/log.h"
 
 #include "vm/flags.h"
 #include "vm/thread.h"
 
 namespace dart {
 
 DEFINE_FLAG(bool, force_log_flush, false, "Always flush log messages.");
 
 DEFINE_FLAG(charp, isolate_log_filter, NULL,
             "Log isolates whose name include the filter. "
-            "Default: service isolate log messages are suppressed.");
+            "Default: service isolate log messages are suppressed "
+            "(specify 'vm-service' to log them).");
 
 Log::Log(LogPrinter printer)
     : printer_(printer),
       manual_flush_(0),
       buffer_(0) {
 }
 
 
 Log::~Log() {
   // Did someone enable manual flushing and then forgot to Flush?
@@ skipping 135 matching lines @@
   log_->EnableManualFlush();
 }
 
 
 LogBlock::~LogBlock() {
   log_->Flush(cursor_);
   log_->DisableManualFlush();
 }
 
 }  // namespace dart