chromeos: changes Window Service to only install EventRewriter in mash

In mus-mode chrome/ash installs the EventRewriterChromeOS, so the
Window Service shouldn't install it too. The Window Service installed
it in such a way that sticky keys wasn't present, which meant the
EventRewriterChromeOS in the WindowService would change the event so
that when the EventRewriterChromeOS in chrome saw the event it didn't
match.

BUG=821592
TEST=covered by tests

Change-Id: Ib5472243bdd0365cd0fc75b31f31faf2aca4e03a
Reviewed-on: https://chromium-review.googlesource.com/962714Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Commit-Queue: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#543106}

services/ui/ws/display_manager.cc

@@ -38,17 +38,17 @@ namespace ui {
 namespace ws {
 
 DisplayManager::DisplayManager(WindowServer* window_server)
-    // |next_root_id_| is used as the lower bits, so that starting at 0 is
-    // fine. |next_display_id_| is used by itself, so we start at 1 to reserve
-    // 0 as invalid.
     : window_server_(window_server),
       cursor_location_manager_(std::make_unique<CursorLocationManager>()) {
 #if defined(OS_CHROMEOS)
-  // TODO: http://crbug.com/701468 fix function key preferences and sticky keys.
-  ui::EventRewriterChromeOS::Delegate* delegate = nullptr;
-  ui::EventRewriter* sticky_keys_controller = nullptr;
-  event_rewriter_ = std::make_unique<ui::EventRewriterChromeOS>(
-      delegate, sticky_keys_controller);
+  if (window_server->is_hosting_viz()) {
+    // TODO: http://crbug.com/701468 fix function key preferences and sticky
+    // keys.
+    ui::EventRewriterChromeOS::Delegate* delegate = nullptr;
+    ui::EventRewriter* sticky_keys_controller = nullptr;
+    event_rewriter_ = std::make_unique<ui::EventRewriterChromeOS>(
+        delegate, sticky_keys_controller);
+  }
 #endif
 }