Adds support for a new target spec: 'mac_xcuitest_bundle'. This allows us to create UI testing bund…

test/mac/xcuitest/TestCase.m

 // Copyright (c) 2013 Google Inc. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #import <XCTest/XCTest.h>
-#import "MyClass.h"
 
 @interface TestCase : XCTestCase
 @end
 
 @implementation TestCase
 - (void)testFoo {
-  MyClass *foo = [[MyClass alloc] init];
+  XCUIApplication *foo = [[XCUIApplication alloc] init];
   XCTAssertNotNil(foo, @"expected non-nil object");
 }
 @end