Oilpan: Query stack frame register instead of manual bookkeeping

Source/platform/heap/Visitor.cpp

 /*
  * Copyright (C) 2014 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 25 matching lines @@
 
 namespace blink {
 
 // gcInfoIndex should start from 1.
 // Since atomicIncrement(&s_gcInfoIndex) (which is defined in
 // RETURN_GCINFO_INDEX) returns an incremented value of s_gcInfoIndex,
 // the initial value of s_gcInfoIndex should be set to 0.
 int s_gcInfoIndex = 0;
 GCInfo const** s_gcInfoTable = nullptr;
 
-int Visitor::m_traceDepth = 0;
+StackFrameDepth* Visitor::m_traceDepth = nullptr;
 
 #if ENABLE(ASSERT)
 void assertObjectHasGCInfo(const void* payload, size_t gcInfoIndex)
 {
     HeapObjectHeader::fromPayload(payload)->checkHeader();
 #if !defined(COMPONENT_BUILD)
     // On component builds we cannot compare the gcInfos as they are statically
     // defined in each of the components and hence will not match.
     BaseHeapPage* page = pageFromObject(payload);
     ASSERT(page->orphaned() || HeapObjectHeader::fromPayload(payload)->gcInfoIndex() == gcInfoIndex);
 #endif
 }
 #endif
 
 }