Fix browser tests on Mac

headless/lib/headless_browser_browsertest.cc

Index: headless/lib/headless_browser_browsertest.cc
diff --git a/headless/lib/headless_browser_browsertest.cc b/headless/lib/headless_browser_browsertest.cc
index 6561339d51eca2405d2c3a9a6a492d33b3668c42..52931af4ab572171d84414386a5db3452cdde53e 100644
--- a/headless/lib/headless_browser_browsertest.cc
+++ b/headless/lib/headless_browser_browsertest.cc
@@ -379,8 +379,12 @@ IN_PROC_BROWSER_TEST_F(HeadlessBrowserTest, DefaultSizes) {
                   ->GetValue()
                   ->GetAsInteger(&window_height));
 
+#if !defined(OS_MACOSX)
+  // On Mac headless does not override the screen dimensions, so they are
+  // left with the actual screen values.
   EXPECT_EQ(kDefaultOptions.window_size.width(), screen_width);
   EXPECT_EQ(kDefaultOptions.window_size.height(), screen_height);
+#endif  // !defined(OS_MACOSX)
   EXPECT_EQ(kDefaultOptions.window_size.width(), window_width);
   EXPECT_EQ(kDefaultOptions.window_size.height(), window_height);
 }