Add a row in the network tray to inform users to turn Bluetooth on to enable Tether.

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 b19b3a037f01bea33f1314c3f41a6f163b78d60d..b1ce16d882d8d694e78d9d7c4fe10ae829a811d3 100644
--- a/ash/system/network/network_icon.cc
+++ b/ash/system/network/network_icon.cc
@@ -876,10 +876,15 @@ int GetMobileUninitializedMsg() {
   static int s_uninitialized_msg(0);
 
   NetworkStateHandler* handler = NetworkHandler::Get()->network_state_handler();
-  if (handler->GetTechnologyState(NetworkTypePattern::Mobile()) ==
+  // TODO(lesliewatkins): Only return this message when Tether is uninitialized
+  // due to no Bluetooth (dependent on codereview.chromium.org/2969493002/).
+  if (handler->GetTechnologyState(NetworkTypePattern::Tether()) ==
       NetworkStateHandler::TECHNOLOGY_UNINITIALIZED) {
-    // TODO (lesliewatkins): Add a more descriptive message (e.g. "Enable
-    // Bluetooth") for Tether technology type.
+    s_uninitialized_msg = IDS_ASH_STATUS_TRAY_ENABLE_BLUETOOTH;
+    s_uninitialized_state_time = base::Time::Now();
+    return s_uninitialized_msg;
+  } else if (handler->GetTechnologyState(NetworkTypePattern::Mobile()) ==
+             NetworkStateHandler::TECHNOLOGY_UNINITIALIZED) {
     s_uninitialized_msg = IDS_ASH_STATUS_TRAY_INITIALIZING_CELLULAR;
     s_uninitialized_state_time = base::Time::Now();
     return s_uninitialized_msg;