Fix race condition with HasMutatorThread that was being used without a lock.

runtime/vm/compiler.cc

 // Copyright (c) 2012, 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/compiler.h"
 
 #include "vm/assembler.h"
 
 #include "vm/ast_printer.h"
 #include "vm/block_scheduler.h"
@@ skipping 1856 matching lines @@
             Compiler::CompileOptimizedFunction(thread,
                                                function,
                                                Compiler::kNoOSRDeoptId));
         // TODO(srdjan): We do not expect errors while compiling optimized
         // code, any errors should have been caught when compiling
         // unoptimized code. Any issues while optimizing are flagged by
         // making the result invalid.
         ASSERT(error.IsNull());
 #ifndef PRODUCT
         Isolate* isolate = thread->isolate();
-        // We cannot aggregate stats if isolate is shutting down.
-        if (isolate->HasMutatorThread()) {
-          isolate->aggregate_compiler_stats()->Add(*thread->compiler_stats());
-        }
+        isolate->aggregate_compiler_stats()->Add(*thread->compiler_stats());
         thread->compiler_stats()->Clear();
 #endif  // PRODUCT
 
         QueueElement* qelem = NULL;
         { MonitorLocker ml(queue_monitor_);
           if (function_queue()->IsEmpty()) {
             // We are shutting down, queue was cleared.
             function = Function::null();
           } else {
             qelem = function_queue()->Remove();
@@ skipping 291 matching lines @@
 
 
 bool BackgroundCompiler::IsDisabled() {
   UNREACHABLE();
   return true;
 }
 
 #endif  // DART_PRECOMPILED_RUNTIME
 
 }  // namespace dart