Simplify layout of tray items and fix spacing for MD.

ash/common/system/tray/system_tray.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ash/common/system/tray/system_tray.h"
 
 #include "ash/common/key_event_watcher.h"
 #include "ash/common/login_status.h"
 #include "ash/common/material_design/material_design_controller.h"
 #include "ash/common/session/session_state_delegate.h"
@@ skipping 164 matching lines @@
       hide_notifications_(false),
       full_system_tray_menu_(false),
       tray_accessibility_(nullptr),
       tray_audio_(nullptr),
       tray_cast_(nullptr),
       tray_date_(nullptr),
       tray_update_(nullptr),
       screen_capture_tray_item_(nullptr),
       screen_share_tray_item_(nullptr) {
   SetContentsBackground();
+  if (MaterialDesignController::IsSystemTrayMenuMaterial())
+    tray_container()->SetMargin(GetTrayConstant(TRAY_IMAGE_ITEM_PADDING), 0);
 }
 
 SystemTray::~SystemTray() {
   // Destroy any child views that might have back pointers before ~View().
   activation_observer_.reset();
   key_event_watcher_.reset();
   system_bubble_.reset();
   notification_bubble_.reset();
   for (std::vector<SystemTrayItem*>::iterator it = items_.begin();
        it != items_.end(); ++it) {
@@ skipping 694 matching lines @@
           .work_area()
           .height();
   if (work_area_height > 0) {
     UMA_HISTOGRAM_CUSTOM_COUNTS(
         "Ash.SystemMenu.PercentageOfWorkAreaHeightCoveredByMenu",
         100 * bubble_view->height() / work_area_height, 1, 300, 100);
   }
 }
 
 }  // namespace ash