Mac: Make clang compile unit_tests.

chrome/browser/cocoa/hover_image_button_unittest.mm

 // Copyright (c) 2009 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #import <Cocoa/Cocoa.h>
 
 #include "app/resource_bundle.h"
 #include "base/scoped_nsobject.h"
 #import "chrome/browser/cocoa/cocoa_test_helper.h"
 #import "chrome/browser/cocoa/hover_image_button.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "testing/platform_test.h"
 #include "grit/theme_resources.h"
 
 namespace {
 
 class HoverImageButtonTest : public CocoaTest {
  public:
   HoverImageButtonTest() {
     NSRect content_frame = [[test_window() contentView] frame];
     scoped_nsobject<HoverImageButton> button(
         [[HoverImageButton alloc] initWithFrame:content_frame]);
-    NSRect frame = NSMakeRect(0, 0, 30, 30);
     button_ = button.get();
     [[test_window() contentView] addSubview:button_];
   }
 
   virtual void SetUp() {
     CocoaTest::BootstrapCocoa();
   }
 
   HoverImageButton* button_;
 };
@@ skipping 25 matching lines @@
 
   [button_ mouseEntered:nil];
   [button_ drawRect:[button_ frame]];
   EXPECT_EQ([button_ alphaValue], 1.0);
   [button_ mouseExited:nil];
   [button_ drawRect:[button_ frame]];
   EXPECT_EQ([button_ alphaValue], 0.5);
 }
 
 }  // namespace