Fix for issue 25236

runtime/vm/thread.h

 // 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.
 
 #ifndef VM_THREAD_H_
 #define VM_THREAD_H_
 
 #include "include/dart_api.h"
 #include "vm/globals.h"
 #include "vm/handles.h"
@@ skipping 104 matching lines @@
   // The currently executing thread, or NULL if not yet initialized.
   static Thread* Current() {
     BaseThread* thread = OSThread::GetCurrentTLS();
     if (thread == NULL || thread->is_os_thread()) {
       return NULL;
     }
     return reinterpret_cast<Thread*>(thread);
   }
 
   // Makes the current thread enter 'isolate'.
-  static void EnterIsolate(Isolate* isolate);
+  static bool EnterIsolate(Isolate* isolate);
   // Makes the current thread exit its isolate.
   static void ExitIsolate();
 
   // A VM thread other than the main mutator thread can enter an isolate as a
   // "helper" to gain limited concurrent access to the isolate. One example is
   // SweeperTask (which uses the class table, which is copy-on-write).
   // TODO(koda): Properly synchronize heap access to expand allowed operations.
-  static void EnterIsolateAsHelper(Isolate* isolate,
+  static bool EnterIsolateAsHelper(Isolate* isolate,
                                    bool bypass_safepoint = false);
   static void ExitIsolateAsHelper(bool bypass_safepoint = false);
 
   // Called when the current thread transitions from mutator to collector.
   // Empties the store buffer block into the isolate.
   // TODO(koda): Always run GC in separate thread.
   static void PrepareForGC();
 
   // OSThread corresponding to this thread.
   OSThread* os_thread() const { return os_thread_; }
@@ skipping 354 matching lines @@
 // Disable thread interrupts.
 class DisableThreadInterruptsScope : public StackResource {
  public:
   explicit DisableThreadInterruptsScope(Thread* thread);
   ~DisableThreadInterruptsScope();
 };
 
 }  // namespace dart
 
 #endif  // VM_THREAD_H_