Unified: unset background color of proxy warning.

This CL fixes wrong background color of proxy warning
("Network may be monitored") in UnifiedSystemTray.

TEST=manual
BUG=870913

Change-Id: Id0a460652ee8431db947cc19aa49c61c434cf5cb
Reviewed-on: https://chromium-review.googlesource.com/1177088Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Commit-Queue: Tetsui Ohkubo <tetsui@chromium.org>
Cr-Commit-Position: refs/heads/master@{#583920}

ash/system/network/network_list.cc

@@ -8,6 +8,7 @@
 #include <utility>
 
 #include "ash/metrics/user_metrics_recorder.h"
+#include "ash/public/cpp/ash_features.h"
 #include "ash/public/cpp/ash_view_ids.h"
 #include "ash/resources/vector_icons/vector_icons.h"
 #include "ash/session/session_controller.h"
@@ -947,8 +948,10 @@ TriView* NetworkListView::CreateConnectionWarning() {
   // Set up layout and apply sticky row property.
   TriView* connection_warning = TrayPopupUtils::CreateDefaultRowView();
   TrayPopupUtils::ConfigureAsStickyHeader(connection_warning);
-  connection_warning->SetBackground(
-      views::CreateSolidBackground(kHeaderBackgroundColor));
+  if (!features::IsSystemTrayUnifiedEnabled()) {
+    connection_warning->SetBackground(
+        views::CreateSolidBackground(kHeaderBackgroundColor));
+  }
 
   // Set 'info' icon on left side.
   views::ImageView* image_view = TrayPopupUtils::CreateMainImageView();