Add tests for zero conversion on Array#indexOf and Array#lastIndexOf

Fixes #435

test/built-ins/Array/prototype/indexOf/fromindex-zero-conversion.js

+// Copyright 2016 The V8 project authors. All rights reserved.
+// This code is governed by the license found in the LICENSE file.
+/*---
+id: sec-array.prototype.indexof
+description: >
+  Return +0 when fromIndex is -0 and return index refers to the first position
+info: >
+  22.1.3.12 Array.prototype.indexOf ( searchElement [ , fromIndex ] )
+
+  ...
+  6. If n ≥ 0, then
+    a. If n is -0, let k be +0; else let k be n.
+  ...
+---*/
+
+assert.sameValue(1 / [true].indexOf(true, -0), +Infinity)

test/built-ins/Array/prototype/lastIndexOf/fromindex-zero-conversion.js

+// Copyright 2016 The V8 project authors. All rights reserved.
+// This code is governed by the license found in the LICENSE file.
+/*---
+id: sec-array.prototype.lastindexof
+description: >
+  Return +0 when fromIndex is -0 and return index refers to the first position
+info: >
+  22.1.3.15 Array.prototype.lastIndexOf ( searchElement [ , fromIndex ] )
+
+  ...
+  5. If n ≥ 0, then
+    a. If n is -0, let k be +0; else let k be min(n, len - 1).
+  ...
+---*/
+
+assert.sameValue(1 / [true].lastIndexOf(true, -0), +Infinity);