[V8][asm.js] Fixes a bug in comma-expression validation.

test/mjsunit/asm/b5528-comma.js

+// Copyright 2016 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.
+
+function Module(stdlib, env, heap) {
+  "use asm";
+
+  var a = new stdlib.Int32Array(heap);
+  var b = new stdlib.Float32Array(heap);
+  var fround = stdlib.Math.fround;
+  var value = env.value|0;
+
+  function foo() {
+    var x = fround(0.0);
+    x = (a[0]=value|0,fround(b[0]));
+    return fround(x);
+  }
+
+  return { foo: foo };
+}
+
+var buffer = new ArrayBuffer(32);
+assertEquals(0.0, Module(this, {value: 0x00000000}, buffer).foo());
+assertEquals(-0.0, Module(this, {value: 0x80000000}, buffer).foo());
+assertEquals(5.0, Module(this, {value: 0x40a00000}, buffer).foo());
+assertEquals(-5.0, Module(this, {value: 0xc0a00000}, buffer).foo());
+assertEquals(129.375, Module(this, {value: 0x43016000}, buffer).foo());
+assertEquals(-129.375, Module(this, {value: 0xc3016000}, buffer).foo());
+assertEquals(Infinity, Module(this, {value: 0x7f800000}, buffer).foo());
+assertEquals(-Infinity, Module(this, {value: 0xff800000}, buffer).foo());
+assertEquals(NaN, Module(this, {value: 0x7fffffff}, buffer).foo());