Oilpan: Implement a GC to take a heap snapshot

Source/platform/heap/Heap.h

Index: Source/platform/heap/Heap.h
diff --git a/Source/platform/heap/Heap.h b/Source/platform/heap/Heap.h
index 2365632741e4b20576cf2db71237d027adc48395..e659551b04ef9f10ab7afe3e3f02724244d64677 100644
--- a/Source/platform/heap/Heap.h
+++ b/Source/platform/heap/Heap.h
@@ -430,7 +430,6 @@ public:
 
     void markAsUnswept()
     {
-        ASSERT(m_swept);
         m_swept = false;
     }
 
@@ -692,7 +691,7 @@ public:
 #endif
 
     virtual void clearFreeLists() { }
-    void makeConsistentForSweeping();
+    void makeConsistentForSweeping(ThreadState::GCType);
 #if ENABLE(ASSERT)
     virtual bool isConsistentForSweeping() = 0;
 #endif
@@ -924,7 +923,7 @@ public:
     static void globalWeakProcessing(Visitor*);
     static void setForcePreciseGCForTesting();
 
-    static void preGC();
+    static void preGC(ThreadState::GCType);
     static void postGC(ThreadState::GCType);
 
     // Conservatively checks whether an address is a pointer in any of the