Handle no cellular device more gracefully in choose-mobile-network UI.

chrome/browser/ui/webui/chromeos/choose_mobile_network_ui.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 "chrome/browser/ui/webui/chromeos/choose_mobile_network_ui.h"
 
 #include <stddef.h>
 
 #include <memory>
 #include <set>
@@ skipping 118 matching lines @@
     : is_page_ready_(false),
       scanning_(false),
       has_pending_results_(false) {
   NetworkStateHandler* handler = GetNetworkStateHandler();
   const DeviceState* cellular =
       handler->GetDeviceStateByType(NetworkTypePattern::Cellular());
   if (!cellular) {
     NET_LOG_ERROR(
         "A cellular device is not available.",
         "Cannot initiate a cellular network scan without a cellular device.");
+    // If there is no cellular device, we set |has_pending_results_| to true so
+    // that HandlePageReady() will show "No networks found." on the web UI.
+    has_pending_results_ = true;
     return;
   }
   handler->AddObserver(this, FROM_HERE);
   device_path_ = cellular->path();
   GetNetworkDeviceHandler()->ProposeScan(
       device_path_,
       base::Bind(&base::DoNothing),
       base::Bind(&NetworkOperationErrorCallback, "ProposeScan"));
 }
 
@@ skipping 65 matching lines @@
   }
 }
 
 void ChooseMobileNetworkHandler::HandleCancel(const base::ListValue* args) {
   const size_t kConnectParamCount = 0;
   if (args->GetSize() != kConnectParamCount) {
     NOTREACHED();
     return;
   }
 
+  if (device_path_.empty())
+    return;
+
   // Switch to automatic mode.
   GetNetworkDeviceHandler()->RegisterCellularNetwork(
       device_path_,
       "",  // An empty string is for registration with the home network.
       base::Bind(&base::DoNothing),
       base::Bind(&NetworkOperationErrorCallback,
                  "Register in automatic mode."));
 }
 
 void ChooseMobileNetworkHandler::HandleConnect(const base::ListValue* args) {
@@ skipping 35 matching lines @@
 ChooseMobileNetworkUI::ChooseMobileNetworkUI(content::WebUI* web_ui)
     : WebUIController(web_ui) {
   web_ui->AddMessageHandler(base::MakeUnique<ChooseMobileNetworkHandler>());
   // Set up the "chrome://choose-mobile-network" source.
   Profile* profile = Profile::FromWebUI(web_ui);
   content::WebUIDataSource::Add(
       profile, CreateChooseMobileNetworkUIHTMLSource());
 }
 
 }  // namespace chromeos