Prepare fullscreen_chromeos.cc to be used for ozone builds.

chrome/browser/BUILD.gn

Index: chrome/browser/BUILD.gn
diff --git a/chrome/browser/BUILD.gn b/chrome/browser/BUILD.gn
index fbcb0a7ad50ae5ac7520d9b897d5063b5b239d50..0fa9593adeba0a0c86dc68c1c607e741865b0cca 100644
--- a/chrome/browser/BUILD.gn
+++ b/chrome/browser/BUILD.gn
@@ -382,7 +382,6 @@ split_static_library("browser") {
     "file_select_helper.h",
     "file_select_helper_mac.mm",
     "fullscreen.h",
-    "fullscreen_chromeos.cc",
     "fullscreen_mac.mm",
     "fullscreen_win.cc",
     "geolocation/chrome_access_token_store.cc",
@@ -3540,6 +3539,14 @@ split_static_library("browser") {
     }
   }
 
+  # Chrome built with 'use_ozone=true' runs today within the mash environment,
+  # so for now the chromeos/ash implementation is (ab)used.
+  # TODO(tonikitoo): Make sure this is factored out when http://crbug.com/585570
+  # is fixed.
+  if (is_chromeos || use_ozone) {
+    sources += [ "fullscreen_ash.cc" ]
+  }
+
   if (android_java_ui) {
     deps += [ "//third_party/WebKit/public:android_mojo_bindings" ]
   }