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 fdf24de7de2a5a962ffc337dedc6b423320e5e84..ca261e1bea17f00fb51c58cd6082f502b2e9d6ff 100644
--- a/Source/platform/heap/Heap.h
+++ b/Source/platform/heap/Heap.h
@@ -386,6 +386,7 @@ public:
     virtual void removeFromHeap() = 0;
     virtual void sweep() = 0;
     virtual void makeConsistentForGC() = 0;
+    virtual void makeConsistentForMutator() = 0;
 #if defined(ADDRESS_SANITIZER)
     virtual void poisonUnmarkedObjects() = 0;
 #endif
@@ -473,6 +474,7 @@ public:
     virtual void removeFromHeap() override;
     virtual void sweep() override;
     virtual void makeConsistentForGC() override;
+    virtual void makeConsistentForMutator() override;
 #if defined(ADDRESS_SANITIZER)
     virtual void poisonUnmarkedObjects() override;
 #endif
@@ -535,6 +537,7 @@ public:
     virtual void removeFromHeap() override;
     virtual void sweep() override;
     virtual void makeConsistentForGC() override;
+    virtual void makeConsistentForMutator() override;
 #if defined(ADDRESS_SANITIZER)
     virtual void poisonUnmarkedObjects() override;
 #endif
@@ -693,6 +696,7 @@ public:
 
     virtual void clearFreeLists() { }
     void makeConsistentForGC();
+    void makeConsistentForMutator();
 #if ENABLE(ASSERT)
     virtual bool isConsistentForGC() = 0;
 #endif