Add a test for OptimizingCompileDispatcher::Flush's non-blocking behavior

src/base/atomic-utils.h

 // Copyright 2015 the V8 project 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 V8_ATOMIC_UTILS_H_
 #define V8_ATOMIC_UTILS_H_
 
 #include <limits.h>
 
 #include "src/base/atomicops.h"
@@ skipping 13 matching lines @@
     return static_cast<T>(base::Barrier_AtomicIncrement(
         &value_, static_cast<base::AtomicWord>(increment)));
   }
 
   // Returns the value after decrementing.
   V8_INLINE T Decrement(T decrement) {
     return static_cast<T>(base::Barrier_AtomicIncrement(
         &value_, -static_cast<base::AtomicWord>(decrement)));
   }
 
-  V8_INLINE T Value() { return static_cast<T>(base::Acquire_Load(&value_)); }
+  V8_INLINE T Value() const {
+    return static_cast<T>(base::Acquire_Load(&value_));
+  }
 
   V8_INLINE void SetValue(T new_value) {
     base::Release_Store(&value_, static_cast<base::AtomicWord>(new_value));
   }
 
   V8_INLINE T operator=(T value) {
     SetValue(value);
     return value;
   }
 
@@ skipping 200 matching lines @@
     return static_cast<base::AtomicWord>(1) << element;
   }
 
   base::AtomicWord bits_;
 };
 
 }  // namespace base
 }  // namespace v8
 
 #endif  // #define V8_ATOMIC_UTILS_H_