Oilpan: move "forced GC" handling back to gcEpilogue().

Source/platform/heap/ThreadState.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 799 matching lines @@
     m_gcState = gcState;
 }
 
 #undef VERIFY_STATE_TRANSITION
 
 ThreadState::GCState ThreadState::gcState() const
 {
     return m_gcState;
 }
 
-void ThreadState::didV8MajorGC(bool forceGC)
+void ThreadState::didV8MajorGC()
 {
     checkThread();
     if (isMainThread()) {
         // Lower the estimated live object size because the V8 major GC is
         // expected to have collected a lot of DOM wrappers and dropped
         // references to their DOM objects.
         Heap::setEstimatedLiveObjectSize(Heap::estimatedLiveObjectSize() / 2);
 
-        if (forceGC) {
-            // This single GC is not enough for two reasons:
-            //   (1) The GC is not precise because the GC scans on-stack pointers conservatively.
-            //   (2) One GC is not enough to break a chain of persistent handles. It's possible that
-            //       some heap allocated objects own objects that contain persistent handles
-            //       pointing to other heap allocated objects. To break the chain, we need multiple GCs.
-            //
-            // Regarding (1), we force a precise GC at the end of the current event loop. So if you want
-            // to collect all garbage, you need to wait until the next event loop.
-            // Regarding (2), it would be OK in practice to trigger only one GC per gcEpilogue, because
-            // GCController.collectAll() forces 7 V8's GC.
-            Heap::collectGarbage(ThreadState::HeapPointersOnStack, ThreadState::GCWithSweep, Heap::ForcedGC);
-
-            // Forces a precise GC at the end of the current event loop.
-            ThreadState::current()->setGCState(ThreadState::FullGCScheduled);
-            return;
-        }
-
         // If under memory pressure, complete sweeping before initiating
         // the urgent conservative GC.
         if (shouldForceMemoryPressureGC())
             completeSweep();
 
         // Schedule an Oilpan GC to avoid the following scenario:
         // (1) A DOM object X holds a v8::Persistent to a V8 object.
         //     Assume that X is small but the V8 object is huge.
         //     The v8::Persistent is released when X is destructed.
         // (2) X's DOM wrapper is created.
@@ skipping 624 matching lines @@
         json->beginArray(it->key.ascii().data());
         for (size_t age = 0; age <= maxHeapObjectAge; ++age)
             json->pushInteger(it->value.ages[age]);
         json->endArray();
     }
     TRACE_EVENT_OBJECT_SNAPSHOT_WITH_ID(TRACE_DISABLED_BY_DEFAULT("blink_gc"), statsName, this, json.release());
 }
 #endif
 
 } // namespace blink