Eliminate USE_ASH macro and replace with OS_CHROMEOS

We have not shipped Windows Ash for years. There is a 1:1 mapping
between USE_ASH and OS_CHROMEOS, so consolidate them.

The BUILD.gn files will be cleaned up separately.

Bug: 673826
Test: compiles, gn check on Chrome OS, Linux and Linux Ozone
Cq-Include-Trybots: master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Change-Id: I5ebf64a133d1032f0d7864ed1a180d0f0b170da1
Reviewed-on: https://chromium-review.googlesource.com/692699
Commit-Queue: James Cook <[email protected]>
Reviewed-by: Scott Violet <[email protected]>
Cr-Commit-Position: refs/heads/master@{#506410}
diff --git a/chrome/browser/prefs/browser_prefs.cc b/chrome/browser/prefs/browser_prefs.cc
index 4df98650..8fd4914 100644
--- a/chrome/browser/prefs/browser_prefs.cc
+++ b/chrome/browser/prefs/browser_prefs.cc
@@ -258,6 +258,10 @@
 #include "chrome/browser/ui/app_list/arc/arc_app_list_prefs.h"
 #endif
 
+#if defined(OS_CHROMEOS)
+#include "chrome/browser/ui/ash/chrome_launcher_prefs.h"
+#endif
+
 #if defined(OS_MACOSX)
 #include "chrome/browser/ui/cocoa/apps/quit_with_apps_controller_mac.h"
 #include "chrome/browser/ui/cocoa/confirm_quit.h"
@@ -279,10 +283,6 @@
 #include "chrome/browser/ui/browser_view_prefs.h"
 #endif
 
-#if defined(USE_ASH)
-#include "chrome/browser/ui/ash/chrome_launcher_prefs.h"
-#endif
-
 #if !defined(OS_ANDROID)
 #include "chrome/browser/ui/webui/md_history_ui.h"
 #include "chrome/browser/ui/webui/settings/md_settings_ui.h"
@@ -638,7 +638,7 @@
   RegisterInvertBubbleUserPrefs(registry);
 #endif
 
-#if defined(USE_ASH)
+#if defined(OS_CHROMEOS)
   RegisterChromeLauncherUserPrefs(registry);
 #endif