Address Siva's comments from https://codereview.chromium.org/1877973002/

runtime/vm/isolate.cc

 // Copyright (c) 2013, 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/isolate.h"
 
 #include "include/dart_api.h"
 #include "include/dart_native_api.h"
 #include "platform/assert.h"
 #include "platform/text_buffer.h"
@@ skipping 1509 matching lines @@
     ISOLATE_METRIC_LIST(ISOLATE_METRIC_PRINT);
 #undef ISOLATE_METRIC_PRINT
     THR_Print("\n");
   }
 }
 
 
 void Isolate::StopBackgroundCompiler() {
   // Wait until all background compilation has finished.
   if (background_compiler_ != NULL) {
-    BackgroundCompiler::Stop(background_compiler_);
+    BackgroundCompiler::Stop(this);
   }
 }
 
 
 void Isolate::Shutdown() {
   ASSERT(this == Isolate::Current());
   StopBackgroundCompiler();
 
 #if defined(DEBUG)
   if (heap_ != NULL) {
@@ skipping 357 matching lines @@
   if (disabling_field_list_ == GrowableObjectArray::null()) {
     disabling_field_list_ = GrowableObjectArray::New(Heap::kOld);
   }
   const GrowableObjectArray& array =
       GrowableObjectArray::Handle(disabling_field_list_);
   array.Add(field, Heap::kOld);
 }
 
 
 RawField* Isolate::GetDisablingField() {
-  ASSERT(Compiler::IsBackgroundCompilation());
-  MutexLocker ml(field_list_mutex_);
+  ASSERT(Compiler::IsBackgroundCompilation() &&
+         (!Isolate::Current()->HasMutatorThread() ||
+         Isolate::Current()->mutator_thread()->IsAtSafepoint()));
+  ASSERT(Thread::Current()->IsAtSafepoint());
   if (disabling_field_list_ == GrowableObjectArray::null()) {
     return Field::null();
   }
   const GrowableObjectArray& array =
       GrowableObjectArray::Handle(disabling_field_list_);
   if (array.Length() == 0) {
     return Field::null();
   }
   return Field::RawCast(array.RemoveLast());
 }
@@ skipping 770 matching lines @@
 void IsolateSpawnState::DecrementSpawnCount() {
   ASSERT(spawn_count_monitor_ != NULL);
   ASSERT(spawn_count_ != NULL);
   MonitorLocker ml(spawn_count_monitor_);
   ASSERT(*spawn_count_ > 0);
   *spawn_count_ = *spawn_count_ - 1;
   ml.Notify();
 }
 
 }  // namespace dart