Refactor OS_LINUX preprocessor directive for LaCrOS effort.

Currently, ChromeOS defines the OS_LINUX directive as well as
OS_CHROMEOS.  We're working to separate these two, so we're
making the fact that OS_LINUX == OS_LINUX || OS_CHROMEOS
explicit.

This is changes for /extensions/browser/api/app_window

This CL was uploaded by git cl split.

R=calamity@chromium.org

Bug: 1110266
Change-Id: I188590d228e449aaebed57a919b175cb2f7674de
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2371294Reviewed-by: calamity <calamity@chromium.org>
Commit-Queue: calamity <calamity@chromium.org>
Cr-Commit-Position: refs/heads/master@{#801278}

extensions/browser/api/app_window/app_window_apitest.cc

@@ -64,7 +64,7 @@ IN_PROC_BROWSER_TEST_F(ExperimentalAppWindowApiTest, SetIcon) {
 #define MAYBE_OnMinimizedEvent OnMinimizedEvent
 #define MAYBE_OnMaximizedEvent OnMaximizedEvent
 #define MAYBE_OnRestoredEvent OnRestoredEvent
-#endif  // defined(OS_LINUX) && !defined(OS_CHROMEOS)
+#endif  // defined(OS_LINUX) || defined(OS_CHROMEOS)
 
 IN_PROC_BROWSER_TEST_F(AppWindowApiTest, MAYBE_OnMinimizedEvent) {
 #if defined(OS_MAC)