Drop thenable coercion cache

src/promise.js

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 "use strict";
 
 // This file relies on the fact that the following declaration has been made
 // in runtime.js:
 // var $Object = global.Object
 // var $WeakMap = global.WeakMap
@@ skipping 186 matching lines @@
     function(x) {
       x = PromiseCoerce(constructor, x);
       return x === that ? onReject(MakeTypeError('promise_cyclic', [x])) :
              IsPromise(x) ? x.then(onResolve, onReject) : onResolve(x);
     },
     onReject,
     PromiseChain
   );
 }
 
-PromiseCoerce.table = new $WeakMap;
-
 function PromiseCoerce(constructor, x) {
   if (!IsPromise(x) && IS_SPEC_OBJECT(x)) {
     var then;
     try {
       then = x.then;
     } catch(r) {
-      var promise = %_CallFunction(constructor, r, PromiseRejected);
-      PromiseCoerce.table.set(x, promise);
-      return promise;
+      return %_CallFunction(constructor, r, PromiseRejected);
     }
-    if (typeof then === 'function') {
-      if (PromiseCoerce.table.has(x)) {
-        return PromiseCoerce.table.get(x);
-      } else {
-        var deferred = %_CallFunction(constructor, PromiseDeferred);
-        PromiseCoerce.table.set(x, deferred.promise);
-        try {
-          %_CallFunction(x, deferred.resolve, deferred.reject, then);
-        } catch(r) {
-          deferred.reject(r);
-        }
-        return deferred.promise;
+    if (IS_SPEC_FUNCTION(then)) {
+      var deferred = %_CallFunction(constructor, PromiseDeferred);
+      try {
+        %_CallFunction(x, deferred.resolve, deferred.reject, then);
+      } catch(r) {
+        deferred.reject(r);
       }
+      return deferred.promise;
     }
   }
   return x;
 }
 
 
 // Combinators.
 
 function PromiseCast(x) {
   // TODO(rossberg): cannot do better until we support @@create.
@@ skipping 70 matching lines @@
 SetUpPromise();
 
 // Functions to expose promise details to the debugger.
 function GetPromiseStatus(promise) {
   return GET_PRIVATE(promise, promiseStatus);
 }
 
 function GetPromiseValue(promise) {
   return GET_PRIVATE(promise, promiseValue);
 }