Expose the content of Maps and WeakMaps through MapMirror.

src/runtime.cc

Index: src/runtime.cc
diff --git a/src/runtime.cc b/src/runtime.cc
index f668ccf15ac9fb3ff9e3a9082943c1a473880276..28a97cb8e201c7881c328a84b72e95dcb1388221 100644
--- a/src/runtime.cc
+++ b/src/runtime.cc
@@ -1688,6 +1688,29 @@ RUNTIME_FUNCTION(Runtime_MapIteratorInitialize) {
 }
 
 
+RUNTIME_FUNCTION(Runtime_GetWeakMapEntries) {
+  HandleScope scope(isolate);
+  ASSERT(args.length() == 1);
+  CONVERT_ARG_HANDLE_CHECKED(JSWeakCollection, holder, 0);
+  Handle<ObjectHashTable> table(ObjectHashTable::cast(holder->table()));
+  Handle<FixedArray> entries =
+      isolate->factory()->NewFixedArray(table->NumberOfElements() * 2);
+  {
+    DisallowHeapAllocation no_gc;
+    int number_of_non_hole_elements = 0;
+    for (int i = 0; i < table->Capacity(); i++) {
+      Handle<Object> key(table->KeyAt(i), isolate);
+      if (table->IsKey(*key)) {
+        entries->set(number_of_non_hole_elements++, *key);
+        entries->set(number_of_non_hole_elements++, table->Lookup(key));
+      }
+    }
+    ASSERT_EQ(table->NumberOfElements() * 2, number_of_non_hole_elements);
+  }
+  return *isolate->factory()->NewJSArrayWithElements(entries);
+}
+
+
 RUNTIME_FUNCTION(Runtime_MapIteratorNext) {
   SealHandleScope shs(isolate);
   ASSERT(args.length() == 2);