Improve ScriptForbiddenScope handling in cross-threaded code.

third_party/WebKit/Source/platform/heap/HeapPage.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 280 matching lines @@
     RELEASE_ASSERT(threadState()->isSweepingInProgress());
 
     // lazySweepPages() can be called recursively if finalizers invoked in
     // page->sweep() allocate memory and the allocation triggers
     // lazySweepPages(). This check prevents the sweeping from being executed
     // recursively.
     if (threadState()->sweepForbidden())
         return nullptr;
 
     TRACE_EVENT0("blink_gc", "BaseHeap::lazySweepPages");
-    ThreadState::SweepForbiddenScope scope(threadState());
+    ThreadState::SweepForbiddenScope sweepForbidden(threadState());
+    ScriptForbiddenIfMainThreadScope scriptForbidden;
+
     double startTime = WTF::currentTimeMS();
-
-    if (threadState()->isMainThread())
-        ScriptForbiddenScope::enter();
-
     Address result = lazySweepPages(allocationSize, gcInfoIndex);
-
-    if (threadState()->isMainThread())
-        ScriptForbiddenScope::exit();
-
     threadState()->accumulateSweepingTime(WTF::currentTimeMS() - startTime);
     Heap::reportMemoryUsageForTracing();
 
     return result;
 }
 
 void BaseHeap::sweepUnsweptPage()
 {
     BasePage* page = m_firstUnsweptPage;
     if (page->isEmpty()) {
@@ skipping 1258 matching lines @@
 
     m_hasEntries = true;
     size_t index = hash(address);
     ASSERT(!(index & 1));
     Address cachePage = roundToBlinkPageStart(address);
     m_entries[index + 1] = m_entries[index];
     m_entries[index] = cachePage;
 }
 
 } // namespace blink