Fix memory leak caused by field type in descriptor array.

test/cctest/test-heap.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 5065 matching lines @@
   // Test that the number-string cache has not been resized in the snapshot.
   CcTest::InitializeVM();
   Isolate* isolate = CcTest::i_isolate();
   if (!isolate->snapshot_available()) return;
   Heap* heap = isolate->heap();
   CHECK_EQ(TestHeap::kInitialNumberStringCacheSize * 2,
            heap->number_string_cache()->length());
 }
 
 
+TEST(Regress3877) {
+  CcTest::InitializeVM();
+  Isolate* isolate = CcTest::i_isolate();
+  Heap* heap = isolate->heap();
+  Factory* factory = isolate->factory();
+  HandleScope scope(isolate);
+  CompileRun("function cls() { this.x = 10; }");
+  Handle<WeakCell> weak_prototype;
+  {
+    HandleScope inner_scope(isolate);
+    v8::Local<v8::Value> result = CompileRun("cls.prototype");
+    Handle<JSObject> proto =
+        v8::Utils::OpenHandle(*v8::Handle<v8::Object>::Cast(result));
+    weak_prototype = inner_scope.CloseAndEscape(factory->NewWeakCell(proto));
+  }
+  CHECK(!weak_prototype->cleared());
+  CompileRun(
+      "var a = { };"
+      "a.x = new cls();"
+      "cls.prototype = null;");
+  for (int i = 0; i < 4; i++) {
+    heap->CollectAllGarbage(Heap::kNoGCFlags);
+  }
+  // The map of a.x keeps prototype alive
+  CHECK(!weak_prototype->cleared());
+  // Change the map of a.x and make the previous map garbage collectable.
+  CompileRun("a.x.__proto__ = {};");
+  for (int i = 0; i < 4; i++) {
+    heap->CollectAllGarbage(Heap::kNoGCFlags);
+  }
+  CHECK(weak_prototype->cleared());
+}
+
+
 #ifdef DEBUG
 TEST(PathTracer) {
   CcTest::InitializeVM();
   v8::HandleScope scope(CcTest::isolate());
 
   v8::Local<v8::Value> result = CompileRun("'abc'");
   Handle<Object> o = v8::Utils::OpenHandle(*result);
   CcTest::i_isolate()->heap()->TracePathToObject(*o);
 }
 #endif  // DEBUG