Move runtime helper for JSWeakCollection onto objects.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index 6d547ef67ac4632056cd84871b183f39cae90ffb..19bd1654d46bf591c5f263a650936d546e3e558d 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -9445,6 +9445,12 @@ class JSWeakCollection: public JSObject {
   // [next]: linked list of encountered weak maps during GC.
   DECL_ACCESSORS(next, Object)
 
+  static void Initialize(Handle<JSWeakCollection> collection, Isolate* isolate);
+  static void Set(Handle<JSWeakCollection> collection, Handle<Object> key,
+                  Handle<Object> value, int32_t hash);
+  static bool Delete(Handle<JSWeakCollection> collection, Handle<Object> key,
+                     int32_t hash);
+
   static const int kTableOffset = JSObject::kHeaderSize;
   static const int kNextOffset = kTableOffset + kPointerSize;
   static const int kSize = kNextOffset + kPointerSize;