Make CUPS USB printing play better with the settings page. This change does several things:

chrome/browser/resources/settings/printing_page/cups_add_printer_dialog.html

 <link rel="import" href="chrome://resources/html/md_select_css.html">
 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/html/web_ui_listener_behavior.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-button/paper-button.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-input/paper-input.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-spinner/paper-spinner.html">
 <link rel="import" href="../i18n_setup.html">
 <link rel="import" href="cups_add_printer_dialog_util.html">
 <link rel="import" href="cups_printers_browser_proxy.html">
 <link rel="import" href="../settings_shared_css.html">
@@ skipping 31 matching lines @@
       }
 
       #manuallyAddPrinterButton {
         -webkit-margin-end: 210px;
       }
     </style>
     <add-printer-dialog>
       <div class="dialog-title">$i18n{addPrintersNearbyTitle}</div>
       <div class="dialog-body">
         <add-printer-list printers="[[discoveredPrinters]]"
-            selected-printer="{{selectedPrinter}}">
+                          new-printer="{{newPrinter}}">

[stevenjb, 2017/04/10 19:49:55]

previous indent was correct

[Carlson, 2017/04/10 22:16:42]

Removed from this changelist

         </add-printer-list>
         <div class="center" id="noPrinterMessage" hidden>
            $i18n{noPrinterNearbyMessage}
         </div>
         <div id="searchSpinner" hidden="[[!discovering_]]">
           <paper-spinner active="[[discovering_]]"></paper-spinner>
           <span>$i18n{searchingNearbyPrinters}</span>
         </div>
       </div>
       <div class="dialog-buttons">
         <paper-button id="manuallyAddPrinterButton"
             on-tap="switchToManualAddDialog_">
           $i18n{manuallyAddPrinterButtonText}
         </paper-button>
         <paper-button class="cancel-button" on-tap="onCancelTap_">
           $i18n{cancelButtonText}
         </paper-button>
         <paper-button class="action-button" id="addPrinterButton"
-            disabled="[[!selectedPrinter]]" on-tap="switchToConfiguringDialog_">
+            disabled="[[!newPrinter]]" on-tap="switchToManufacturerDialog_">
           $i18n{addPrinterButtonText}
         </paper-button>
       </div>
     </add-printer-dialog>
   </template>
 </dom-module>
 
 <dom-module id="add-printer-manually-dialog">
   <template>
     <style include="settings-shared md-select">
@@ skipping 215 matching lines @@
               </paper-input>
             </div>
           </div>
         </div>
         <div class="error-message" hidden="[[!setupFailed]]">
           Driver not found (exact error message TBD)
         </div>
       </div>
       <div class="dialog-buttons">
         <paper-button id="manuallyAddPrinterButton"
             on-tap="switchToManualAddDialog_">

[xdai1, 2017/03/31 23:33:52]

If you want to remove selectedPrinter variable, you might also need to modify
the function switchToManualAddDialog() here.
Suppose the scenario like this: Open discovery dialog, select one printer from
the list, click Add, then the manufacturer-model dialog shows up, select the
manufacturer and model from the drop down list, do nothing and then click on
this manual add printer button. I think the same problem as I described in
previous comment happens.

Note you don't want to simply reset the newPrinter here because if
manufacture-model dialog was opened by the manual-add-printer dialog, resetting
the newPrinter will make you lost all the fields you just entered...

           $i18n{manuallyAddPrinterButtonText}
         </paper-button>
         <paper-button class="cancel-button" on-tap="onCancelTap_">
           $i18n{cancelButtonText}
         </paper-button>
         <paper-button class="action-button" id="addPrinterButton"
             on-tap="switchToConfiguringDialog_">
           $i18n{addPrinterButtonText}
         </paper-button>
       </div>
@@ skipping 23 matching lines @@
     </add-printer-dialog>
   </template>
 </dom-module>
 
 <dom-module id="settings-cups-add-printer-dialog">
   <template>
     <style include="settings-shared"></style>
 
     <!-- Printer Discovery Dialog -->
     <template is="dom-if" if="[[showDiscoveryDialog_]]" restamp>
-      <add-printer-discovery-dialog selected-printer="{{selectedPrinter}}">
+      <add-printer-discovery-dialog new-printer="{{newPrinter}}">
       </add-printer-discovery-dialog>
     </template>
 
     <!-- Manually Add Printer Dialog -->
     <template is="dom-if" if="[[showManuallyAddDialog_]]" restamp>
       <add-printer-manually-dialog new-printer="{{newPrinter}}">
       </add-printer-manually-dialog>
     </template>
 
     <!-- Configuring Printer Dialog -->
     <template is="dom-if" if="[[showConfiguringDialog_]]" restamp>
       <add-printer-configuring-dialog
           printer-name="[[getConfiguringPrinterName_()]]"
           dialog-title="[[configuringDialogTitle]]">
       </add-printer-configuring-dialog>
     </template>
 
     <!-- Manufacturer and Model Dialog -->
     <template is="dom-if" if="[[showManufacturerDialog_]]" restamp>
       <add-printer-manufacturer-model-dialog new-printer="{{newPrinter}}"
           setup-failed="[[setupFailed]]">
       </add-printer-manufacturer-model-dialog>
     </template>
 
   </template>
   <script src="cups_add_printer_dialog.js"></script>
 </dom-module>