Changed default image in NetworkIconImpl to null image.

ash/system/network/network_icon.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/system/network/network_icon.h"
 
 #include "ash/resources/vector_icons/vector_icons.h"
 #include "ash/strings/grit/ash_strings.h"
 #include "ash/system/network/network_icon_animation.h"
 #include "ash/system/network/network_icon_animation_observer.h"
@@ skipping 598 matching lines @@
 //------------------------------------------------------------------------------
 // NetworkIconImpl
 
 NetworkIconImpl::NetworkIconImpl(const std::string& path,
                                  IconType icon_type,
                                  const std::string& network_type)
     : network_path_(path),
       icon_type_(icon_type),
       strength_index_(-1),
       behind_captive_portal_(false) {
-  // Default image
-  image_ = GetBasicImage(false, icon_type, network_type);
+  // Default image is null.

[stevenjb, 2017/05/10 17:02:57]

This is probably fine. Make sure to test both the status area (bottom-right
corner) and the network and VPN lists with active Ethernet, WiFi, VPN, Cellular,
and WiMax connections. You should be able to test most of that except Cellular
on a device, and you can test Cellular on a Linux build by passing in the
following command line argument:

--shill-stub=interactive=1,ethernet=0,wifi=0,cellular=LTE

(Test WiMax with wimax=1 instead of cellular=LTE. It's also a good idea to test
cellular=GSM to test the 3g badge as well).

 }
 
 void NetworkIconImpl::Update(const NetworkState* network) {
   DCHECK(network);
   // Determine whether or not we need to update the icon.
   bool dirty = image_.isNull();
 
   // If the network state has changed, the icon needs updating.
   if (state_ != network->connection_state()) {
     state_ = network->connection_state();
@@ skipping 363 matching lines @@
     network_paths.insert((*iter)->path());
   }
   PurgeIconMap(ICON_TYPE_TRAY, network_paths);
   PurgeIconMap(ICON_TYPE_DEFAULT_VIEW, network_paths);
   PurgeIconMap(ICON_TYPE_LIST, network_paths);
   PurgeIconMap(ICON_TYPE_MENU_LIST, network_paths);
 }
 
 }  // namespace network_icon
 }  // namespace ash