use Symbol.for for well-known symbols in modern engines, close #998

CHANGELOG.md

@@ -2,6 +2,7 @@
 ##### Unreleased
 - Most built-ins are encapsulated in `core-js` for preventing possible cases of breaking / observing the internal state by patching / deleting of them
 - Clearing of `Error` stack from extra entries experimentally added to `AggregateError`, [#996](https://github.com/zloirock/core-js/pull/996), in case lack of problems it will be extended to other cases
+- In engines with native `Symbol` support, new well-known symbols created with usage `Symbol.for` for ensuring the same keys in different realms, [#998](https://github.com/zloirock/core-js/issues/998)
 - Added a workaround of [a BrowserFS NodeJS `process` polyfill bug](https://github.com/jvilk/bfs-process/issues/5) that incorrectly reports V8 version that's used in some cases of `core-js` feature detection
 - Fixed normalization of `message` `AggregateError` argument
 - Fixed order of arguments conversion in `Math.scale`, [a spec draft bug](https://github.com/rwaldron/proposal-math-extensions/issues/24)

packages/core-js/internals/well-known-symbol.js

@@ -7,14 +7,18 @@ var USE_SYMBOL_AS_UID = require('../internals/use-symbol-as-uid');
 
 var WellKnownSymbolsStore = shared('wks');
 var Symbol = global.Symbol;
+var symbolFor = Symbol && Symbol['for'];
 var createWellKnownSymbol = USE_SYMBOL_AS_UID ? Symbol : Symbol && Symbol.withoutSetter || uid;
 
 module.exports = function (name) {
   if (!hasOwn(WellKnownSymbolsStore, name) || !(NATIVE_SYMBOL || typeof WellKnownSymbolsStore[name] == 'string')) {
+    var description = 'Symbol.' + name;
     if (NATIVE_SYMBOL && hasOwn(Symbol, name)) {
       WellKnownSymbolsStore[name] = Symbol[name];
+    } else if (USE_SYMBOL_AS_UID && symbolFor) {
+      WellKnownSymbolsStore[name] = symbolFor(description);
     } else {
-      WellKnownSymbolsStore[name] = createWellKnownSymbol('Symbol.' + name);
+      WellKnownSymbolsStore[name] = createWellKnownSymbol(description);
     }
   } return WellKnownSymbolsStore[name];
 };