Array.prototype.{reduce, reduceRight}: Wrong order of operations when determining initial value.

BUG=v8:3534
LOG=
R=svenpanne@chromium.org, wingo@igalia.com

Review URL: https://codereview.chromium.org/614733002

Patch from Diego Pino <dpino@igalia.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24807 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/array.js

@@ -1418,9 +1418,8 @@ function ArrayReduce(callback, current) {
   var i = 0;
   find_initial: if (%_ArgumentsLength() < 2) {
     for (; i < length; i++) {
-      current = array[i];
-      if (!IS_UNDEFINED(current) || i in array) {
-        i++;
+      if (i in array) {
+        current = array[i++];
         break find_initial;
       }
     }
@@ -1455,9 +1454,8 @@ function ArrayReduceRight(callback, current) {
   var i = length - 1;
   find_initial: if (%_ArgumentsLength() < 2) {
     for (; i >= 0; i--) {
-      current = array[i];
-      if (!IS_UNDEFINED(current) || i in array) {
-        i--;
+      if (i in array) {
+        current = array[i--];
         break find_initial;
       }
     }

test/mjsunit/array-reduce.js

@@ -521,3 +521,13 @@ testReduce("reduce", "ArrayManipulationExtender", 10,
             [3, 3, 2, [1, 2, 3, 4, 4, 5], 6],
             [6, 4, 3, [1, 2, 3, 4, 4, 5, 6], 10],
            ], arr, extender, 0);
+
+var arr = [];
+Object.defineProperty(arr, "0", { get: function() { delete this[0] },
+  configurable: true });
+assertEquals(undefined, arr.reduce(function(val) { return val }));
+
+var arr = [];
+Object.defineProperty(arr, "0", { get: function() { delete this[0] },
+  configurable: true});
+assertEquals(undefined, arr.reduceRight(function(val) { return val }));