[turbofan] Tests for simplified lowering of unsigned min/max (it did not have code coverage).

Review-Url: https://codereview.chromium.org/2305523004
Cr-Commit-Position: refs/heads/master@{#39223}

test/mjsunit/compiler/unsigned-min-max.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.
+
+// Flags: --allow-natives-syntax
+
+function umin(a, b) {
+  a = a >>> 0;
+  b = b >>> 0;
+  return Math.min(a, b);
+}
+
+umin(1, 1);
+umin(2, 2);
+%OptimizeFunctionOnNextCall(umin);
+assertEquals(1, umin(1, 2));
+assertEquals(1, umin(2, 1));
+assertEquals(0, umin(0, 4294967295));
+assertEquals(0, umin(4294967295, 0));
+assertEquals(4294967294, umin(-1, -2));
+assertEquals(1234, umin(-2, 1234));
+
+function umax(a, b) {
+  a = a >>> 0;
+  b = b >>> 0;
+  return Math.max(a, b);
+}
+
+umax(1, 1);
+umax(2, 2);
+%OptimizeFunctionOnNextCall(umax);
+assertEquals(2, umax(1, 2));
+assertEquals(2, umax(2, 1));
+assertEquals(4294967295, umax(0, 4294967295));
+assertEquals(4294967295, umax(4294967295, 0));
+assertEquals(4294967295, umax(-1, -2));
+assertEquals(4294967294, umax(-2, 1234));