Remove unmarked entries from per context map caches.

test/cctest/test-api.cc

 // Copyright 2011 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 14641 matching lines @@
   CHECK_EQ(v8_str("DONT_CHANGE"), obj->Get(v8_str("1")));
   obj->Set(v8_num(2), v8_str("DONT_CHANGE"), v8::ReadOnly);
   obj->Set(v8_num(2), v8_str("foobar"));
   CHECK_EQ(v8_str("DONT_CHANGE"), obj->Get(v8_num(2)));
 
   // Test non-smi case.
   obj->Set(v8_str("2000000000"), v8_str("DONT_CHANGE"), v8::ReadOnly);
   obj->Set(v8_str("2000000000"), v8_str("foobar"));
   CHECK_EQ(v8_str("DONT_CHANGE"), obj->Get(v8_str("2000000000")));
 }
+
+
+THREADED_TEST(Regress1516) {
+  v8::HandleScope scope;
+
+  LocalContext context;
+  { v8::HandleScope temp_scope;
+    CompileRun("({'a': 0})");
+  }
+
+  int elements;
+  { i::MapCache* map_cache =
+        i::MapCache::cast(i::Isolate::Current()->context()->map_cache());
+    elements = map_cache->NumberOfElements();
+    CHECK_LE(1, elements);
+  }
+
+  i::Isolate::Current()->heap()->CollectAllGarbage(true);
+  { i::Object* raw_map_cache = i::Isolate::Current()->context()->map_cache();
+    if (raw_map_cache != i::Isolate::Current()->heap()->undefined_value()) {
+      i::MapCache* map_cache = i::MapCache::cast(raw_map_cache);
+      CHECK_GT(elements, map_cache->NumberOfElements());
+    }
+  }
+}