Upgrade Symbol implementation to match current ES6 behavior.

test/cctest/test-api.cc

Index: test/cctest/test-api.cc
diff --git a/test/cctest/test-api.cc b/test/cctest/test-api.cc
index eeb786518e8d6ca13cb5b915505017c925d98573..2c4152110a620925a7a2b53ac2c2bbc4bea82ade 100644
--- a/test/cctest/test-api.cc
+++ b/test/cctest/test-api.cc
@@ -2759,7 +2759,13 @@ THREADED_TEST(SymbolProperties) {
   CHECK(sym_obj->IsSymbolObject());
   CHECK(!sym2->IsSymbolObject());
   CHECK(!obj->IsSymbolObject());
-  CHECK(sym_obj->Equals(sym2));
+  // Comparing Symbol wrapper with Symbol will throw when
+  // ToPrimitive() is attempted performed on the wrapper.
+  {
+    v8::TryCatch try_catch;
+    sym_obj->Equals(sym2);
+    CHECK(try_catch.HasCaught());
+  }
   CHECK(!sym_obj->StrictEquals(sym2));
   CHECK(v8::SymbolObject::Cast(*sym_obj)->Equals(sym_obj));
   CHECK(v8::SymbolObject::Cast(*sym_obj)->ValueOf()->Equals(sym2));