Oilpan: Reduce FIXME(OILPAN) from the code base

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 556 matching lines @@
     // Call weak callbacks on objects that may now be pointing to dead objects.
     while (popAndInvokeGlobalWeakCallback(visitor)) { }
 
     // It is not permitted to trace pointers of live objects in the weak
     // callback phase, so the marking stack should still be empty here.
     ASSERT(s_markingStack->isEmpty());
 }
 
 void Heap::collectAllGarbage()
 {
-    // FIXME: Oilpan: we should perform a single GC and everything
-    // should die. Unfortunately it is not the case for all objects
-    // because the hierarchy was not completely moved to the heap and
-    // some heap allocated objects own objects that contain persistents
-    // pointing to other heap allocated objects.
+    // We need to run multiple GCs to collect a chain of persistent handles.
     size_t previousLiveObjects = 0;
     for (int i = 0; i < 5; ++i) {
         collectGarbage(ThreadState::NoHeapPointersOnStack, ThreadState::GCWithSweep, ForcedGC);
         size_t liveObjects = Heap::markedObjectSize();
         if (liveObjects == previousLiveObjects)
             break;
         previousLiveObjects = liveObjects;
     }
 }
 
@@ skipping 187 matching lines @@
 size_t Heap::s_objectSizeAtLastGC = 0;
 size_t Heap::s_markedObjectSize = 0;
 size_t Heap::s_markedObjectSizeAtLastCompleteSweep = 0;
 size_t Heap::s_persistentCount = 0;
 size_t Heap::s_persistentCountAtLastGC = 0;
 size_t Heap::s_collectedPersistentCount = 0;
 size_t Heap::s_partitionAllocSizeAtLastGC = 0;
 double Heap::s_estimatedMarkingTimePerByte = 0.0;
 
 } // namespace blink