More work for background compilation; move pending_functions_ from ObjectStore to Thread.

runtime/vm/compiler_stats.h

 // Copyright (c) 2011, 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.
 
 #ifndef VM_COMPILER_STATS_H_
 #define VM_COMPILER_STATS_H_
 
 #include "vm/allocation.h"
 #include "vm/flags.h"
 #include "vm/isolate.h"
@@ skipping 55 matching lines @@
   bool use_benchmark_output;
 
   // Update stats that are computed, e.g. token count.
   void Update();
 
   void EnableBenchmark();
   char* BenchmarkOutput();
   char* PrintToZone();
 };
 
-// TODO(hausner): make the increment thread-safe.
 #define INC_STAT(thread, counter, incr)                                        \
   if (FLAG_compiler_stats) {                                                   \
-      (thread)->isolate()->compiler_stats()->counter += (incr); }
+    MutexLocker ml((thread)->isolate()->mutex());                              \
+    (thread)->isolate()->compiler_stats()->counter += (incr);                  \
+  }
 
 #define STAT_VALUE(thread, counter)                                            \
   ((FLAG_compiler_stats != false) ?                                            \
       (thread)->isolate()->compiler_stats()->counter : 0)
 
 #define CSTAT_TIMER_SCOPE(thr, t)                                              \
   TimerScope timer(FLAG_compiler_stats,                                        \
       FLAG_compiler_stats ? &((thr)->isolate()->compiler_stats()->t) : NULL,   \
       thr);
 
 }  // namespace dart
 
 #endif  // VM_COMPILER_STATS_H_