Fastpath some spread-call desugaring.

test/mjsunit/es6/spread-call.js

Index: test/mjsunit/es6/spread-call.js
diff --git a/test/mjsunit/es6/spread-call.js b/test/mjsunit/es6/spread-call.js
index 05e17741d6862886be52ea2abe502bb798716fe8..22d4406d479e91f862367699ff841ec03cadc86d 100644
--- a/test/mjsunit/es6/spread-call.js
+++ b/test/mjsunit/es6/spread-call.js
@@ -346,6 +346,88 @@
   assertEquals("ABXYC1C2DEBXYC1C2", log);
 })();
 
+(function testArrayPrototypeHoleGetterModifiesIteratorPrototypeNext() {
+  function sum() {
+    var sum = arguments[0];
+    for (var i = 1; i < arguments.length; ++i) {
+      sum += arguments[i];
+    }
+    return sum;
+  }
+  var a = [1, 2];
+  a[3] = 4;
+  var called = 0;
+
+  Object.defineProperty(Array.prototype, 2, {
+    get: function() {
+      var ai = a[Symbol.iterator]();
+      var original_next = ai.__proto__["next"];
+      Object.defineProperty(ai.__proto__, "next", {
+        get: function() {
+          called++;
+          return original_next;
+        }
+      });
+      return 3;
+    }
+  });
+
+  assertEquals(10, sum(...a));
+  assertEquals(2, called);
+})();
+
+(function testArrayHasOtherPrototype() {
+  function countArgs() { return arguments.length; }
+  var a = [1, 2, 3];
+  var b = {};
+  Object.defineProperty(b, Symbol.iterator, {
+    value: function*() {
+      yield 4;
+    },
+    configurable: true
+  });
+
+  Object.setPrototypeOf(a, b);
+
+  assertEquals(1, countArgs(...a));
+})();
+
+(function testArrayIteratorPrototypeGetter() {
+  function countArgs() { return arguments.length; }
+  var a = [1, 2, 3];
+  var ai = a[Symbol.iterator]();
+  var called = 0;
+
+  var original_next = ai.__proto__["next"];
+
+  Object.defineProperty(ai.__proto__, "next", {
+    get: function() {
+      called++;
+      return original_next;
+    }
+  });
+
+  countArgs(...a);
+
+  // should be called 4 times; 3 for the values, 1 for the final
+  // {value: undefined, done: true} pair
+  assertEquals(4, called);
+})();
+
+(function testArrayIteratorPrototypeModified() {
+  function countArgs() { return arguments.length; }
+  var a = [1,2,3];
+  var ai = a[Symbol.iterator]();
+  Object.defineProperty(ai.__proto__, "next", {
+    value: function() {
+      return {value: undefined, done: true};
+     },
+     configurable: true
+  });
+
+  assertEquals(0, countArgs(...a));
+
+})();
 
 (function testCustomArrayPrototypeIterator() {
   var origIterator =
@@ -370,3 +452,29 @@
 
   Object.defineProperty(Array.prototype, Symbol.iterator, origIterator);
 })();
+
+(function testGetPropertyIteratorCalledExactlyOnce() {
+  function countArgs() { return arguments.length; }
+  var a = [1, 2, 3];
+  var called = 0;
+
+  Object.defineProperty(Array.prototype, Symbol.iterator, {
+    value: function*() {
+      yield 1;
+      yield 2;
+    },
+    configurable: true
+  });
+
+  var it = a[Symbol.iterator];
+  Object.defineProperty(a, Symbol.iterator, {
+    get: function() {
+      called++;
+      return it;
+    }
+  });
+
+  countArgs(...a);
+
+  assertEquals(1, called);
+})();