Mac: Make clang compile unit_tests.

chrome/browser/cocoa/hover_image_button_unittest.mm

Index: chrome/browser/cocoa/hover_image_button_unittest.mm
diff --git a/chrome/browser/cocoa/hover_image_button_unittest.mm b/chrome/browser/cocoa/hover_image_button_unittest.mm
index 9d063bf9834e4ebfc90c5c8a423b4cfef085ccf5..116a646178363d359b7d46aa14875283fdd099fe 100644
--- a/chrome/browser/cocoa/hover_image_button_unittest.mm
+++ b/chrome/browser/cocoa/hover_image_button_unittest.mm
@@ -20,7 +20,6 @@ class HoverImageButtonTest : public CocoaTest {
     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_];
   }