Changed default image in NetworkIconImpl to null image.

ash/system/network/network_icon.cc

Index: ash/system/network/network_icon.cc
diff --git a/ash/system/network/network_icon.cc b/ash/system/network/network_icon.cc
index fbccbbfecae3ed83e3557299be579402c6d14761..1174c006d687a4ae97b67238cf40d959791da5e5 100644
--- a/ash/system/network/network_icon.cc
+++ b/ash/system/network/network_icon.cc
@@ -616,8 +616,7 @@ NetworkIconImpl::NetworkIconImpl(const std::string& 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) {