Improve ScriptForbiddenScope handling in cross-threaded code.

third_party/WebKit/Source/platform/heap/Heap.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 378 matching lines @@
     // See collectGarbageForTerminatingThread() comment on why a
     // safepoint scope isn't entered for it.
     SafePointScope safePointScope(stackState, gcType != BlinkGC::ThreadTerminationGC ? state : nullptr);
 
     // Try to park the other threads. If we're unable to, bail out of the GC.
     if (!gcScope.parkAllThreads(stackState, gcType))
         return;
 
     // Resume all parked threads upon leaving this scope.
     ResumeThreadScope resumeThreads(gcType);
-
-    if (state->isMainThread())
-        ScriptForbiddenScope::enter();
+    ScriptForbiddenIfMainThreadScope scriptForbidden;
 
     TRACE_EVENT2("blink_gc", "Heap::collectGarbage",
         "lazySweeping", gcType == BlinkGC::GCWithoutSweep,
         "gcReason", gcReasonString(reason));
     TRACE_EVENT_SCOPED_SAMPLING_STATE("blink_gc", "BlinkGC");
     double startTime = WTF::currentTimeMS();
 
     if (gcType == BlinkGC::TakeSnapshot)
         BlinkGCMemoryDumpProvider::instance()->clearProcessDumpForCurrentGC();
 
@@ skipping 42 matching lines @@
     WTF::Partitions::reportMemoryUsageHistogram();
 
     postGC(gcType);
 
 #if ENABLE(ASSERT)
     // 0 is used to figure non-assigned area, so avoid to use 0 in s_gcGeneration.
     if (++s_gcGeneration == 0) {
         s_gcGeneration = 1;
     }
 #endif
-
-    if (state->isMainThread())
-        ScriptForbiddenScope::exit();
 }
 
 void Heap::collectGarbageForTerminatingThread(ThreadState* state)
 {
     {
         // A thread-specific termination GC must not allow other global GCs to go
         // ahead while it is running, hence the termination GC does not enter a
         // safepoint. GCScope will not enter also a safepoint scope for
         // ThreadTerminationGC.
         GCScope gcScope(state, BlinkGC::NoHeapPointersOnStack, BlinkGC::ThreadTerminationGC);
@@ skipping 292 matching lines @@
 size_t Heap::s_wrapperCount = 0;
 size_t Heap::s_wrapperCountAtLastGC = 0;
 size_t Heap::s_collectedWrapperCount = 0;
 size_t Heap::s_partitionAllocSizeAtLastGC = 0;
 double Heap::s_estimatedMarkingTimePerByte = 0.0;
 #if ENABLE(ASSERT)
 uint16_t Heap::s_gcGeneration = 0;
 #endif
 
 } // namespace blink