Enable ES6 Symbols by default

test/mjsunit/debug-script.js

 // Copyright 2008 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 41 matching lines @@
   } else if (scripts[i].type == Debug.ScriptType.Extension) {
     extension_count++;
   } else if (scripts[i].type == Debug.ScriptType.Normal) {
     normal_count++;
   } else {
     assertUnreachable('Unexpected type ' + scripts[i].type);
   }
 }
 
 // This has to be updated if the number of native scripts change.
-assertTrue(named_native_count == 19 || named_native_count == 20);
+assertEquals(21, named_native_count);
 // Only the 'gc' extension is loaded.
 assertEquals(1, extension_count);
 // This script and mjsunit.js has been loaded.  If using d8, d8 loads
 // a normal script during startup too.
 assertTrue(normal_count == 2 || normal_count == 3);
 
 // Test a builtins script.
 var math_script = Debug.findScript('native math.js');
 assertEquals('native math.js', math_script.name);
 assertEquals(Debug.ScriptType.Native, math_script.type);
@@ skipping 16 matching lines @@
 }
 
 // Test a normal script.
 var mjsunit_js_script = Debug.findScript(/mjsunit.js/);
 assertTrue(/mjsunit.js/.test(mjsunit_js_script.name));
 assertEquals(Debug.ScriptType.Normal, mjsunit_js_script.type);
 
 // Check a nonexistent script.
 var dummy_script = Debug.findScript('dummy.js');
 assertTrue(typeof dummy_script == 'undefined');