Use enum for per thread heap enabled flag

third_party/WebKit/Source/platform/heap/BlinkGC.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BlinkGC_h
 #define BlinkGC_h
 
 // BlinkGC.h is a file that defines common things used by Blink GC.
 
 #include "platform/PlatformExport.h"
@@ skipping 83 matching lines @@
         FOR_EACH_TYPED_ARENA(TypedArenaEnumName)
         LargeObjectArenaIndex,
         // Values used for iteration of heap segments.
         NumberOfArenas,
     };
 
     enum V8GCType {
         V8MinorGC,
         V8MajorGC,
     };
+
+    enum ThreadHeapMode {
+        MainThreadHeapMode,
+        PerThreadHeapMode,
+    };
 };
 
 } // namespace blink
 
 #endif