Implement symbol @@hasInstance for ES6 instanceof support.

test/mjsunit/es6/symbols.js

 // Copyright 2013 the V8 project authors. All rights reserved.
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 // modification, are permitted provided that the following conditions are
 // met:
 //
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@@ skipping 423 matching lines @@
 
   for (var i = 0; i < objectOwnSymbols.length; i++) {
     assertEquals(objectOwnSymbols[i], syms[i * 2])
   }
 }
 TestGetOwnPropertySymbolsWithProto()
 
 
 function TestWellKnown() {
   var symbols = [
+    "hasInstance",
     // TODO(rossberg): reactivate once implemented.
-    // "hasInstance", "isConcatSpreadable", "isRegExp",
+    // "isConcatSpreadable", "isRegExp",
     "iterator", /* "toStringTag", */ "unscopables"
   ]
 
   for (var i in symbols) {
     var name = symbols[i]
     var desc = Object.getOwnPropertyDescriptor(Symbol, name)
     assertSame("symbol", typeof desc.value)
     assertSame("Symbol(Symbol." + name + ")", desc.value.toString())
     assertFalse(desc.writable)
     assertFalse(desc.configurable)
@@ skipping 99 matching lines @@
   assertEquals(expected, JSON.stringify(input));
   assertEquals(expected, JSON.stringify(input, null, 0));
 }
 
 TestStringify(undefined, Symbol("a"));
 TestStringify('[{}]', [Object(Symbol())]);
 var symbol_wrapper = Object(Symbol("a"))
 TestStringify('{}', symbol_wrapper);
 symbol_wrapper.a = 1;
 TestStringify('{"a":1}', symbol_wrapper);