Implement IdentityMap<V>, a robust, GC-safe object-identity HashMap.

src/heap/heap.h

Index: src/heap/heap.h
diff --git a/src/heap/heap.h b/src/heap/heap.h
index 7573c676aa14201271684b66a5b7727a95349daf..ed90900877dd84c55dcc3107a5a07c8cecd0bd8d 100644
--- a/src/heap/heap.h
+++ b/src/heap/heap.h
@@ -1451,6 +1451,37 @@ class Heap {
   void TraceObjectStat(const char* name, int count, int size, double time);
   void CheckpointObjectStats();
 
+  struct StrongRootsList {
+    Object** start_;
+    Object** end_;
+    StrongRootsList* next_;
+  };
+
+  void RegisterStrongRoots(Object** start, Object** end) {
+    StrongRootsList* list = new StrongRootsList();
+    list->next_ = strong_roots_list_;
+    list->start_ = start;
+    list->end_ = end;
+    strong_roots_list_ = list;
+  }
+
+  void UnregisterStrongRoots(Object** start) {
+    StrongRootsList* prev = NULL;
+    for (StrongRootsList* list = strong_roots_list_; list; list = list->next_) {
+      if (list->start_ == start) {
+        if (prev) {
+          prev->next_ = list->next_;
+        } else {
+          strong_roots_list_ = list->next_;
+        }
+        delete list;
+      }
+      prev = list;
+    }
+  }
+
+  base::Mutex* relocation_mutex() { return &relocation_mutex_; }
+
   // We don't use a LockGuard here since we want to lock the heap
   // only when FLAG_concurrent_recompilation is true.
   class RelocationLock {
@@ -2151,6 +2182,8 @@ class Heap {
 
   bool concurrent_sweeping_enabled_;
 
+  StrongRootsList* strong_roots_list_;
+
   friend class AlwaysAllocateScope;
   friend class Deserializer;
   friend class Factory;