Revert of Oilpan: Decommit backing storage of CallbackStacks

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

Index: third_party/WebKit/Source/platform/heap/Heap.cpp
diff --git a/third_party/WebKit/Source/platform/heap/Heap.cpp b/third_party/WebKit/Source/platform/heap/Heap.cpp
index 5f2809b0fde544c5063643db8588a1cc4ac1e092..8a414e3ec0378d68a144275f1cf59b6561e47c60 100644
--- a/third_party/WebKit/Source/platform/heap/Heap.cpp
+++ b/third_party/WebKit/Source/platform/heap/Heap.cpp
@@ -355,14 +355,6 @@
 }
 #endif
 
-void Heap::decommitCallbackStacks()
-{
-    s_markingStack->decommit();
-    s_postMarkingCallbackStack->decommit();
-    s_globalWeakCallbackStack->decommit();
-    s_ephemeronStack->decommit();
-}
-
 void Heap::preGC()
 {
     ASSERT(!ThreadState::current()->isInGC());
@@ -477,7 +469,6 @@
     WTF::Partitions::reportMemoryUsageHistogram();
 
     postGC(gcType);
-    Heap::decommitCallbackStacks();
 
 #if ENABLE(ASSERT)
     // 0 is used to figure non-assigned area, so avoid to use 0 in s_gcGeneration.
@@ -520,7 +511,6 @@
         globalWeakProcessing(gcScope.visitor());
 
         state->postGC(BlinkGC::GCWithSweep);
-        Heap::decommitCallbackStacks();
     }
     state->preSweep();
 }
@@ -556,6 +546,8 @@
     // 2. the markNoTracing callbacks on collection backings to mark them
     //    if they are only reachable from their front objects.
     while (popAndInvokePostMarkingCallback(visitor)) { }
+
+    s_ephemeronStack->clear();
 
     // Post-marking callbacks should not trace any objects and
     // therefore the marking stack should be empty after the