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.js

 // Copyright 2016 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.
 
 /**
  * @fileoverview 'settings-cups-add-printer-dialog' includes multiple dialogs to
  * set up a new CUPS printer.
  * Subdialogs include:
  * - 'add-printer-discovery-dialog' is a dialog showing discovered printers on
  *   the network that are available for setup.
@@ skipping 27 matching lines @@
 
   behaviors: [WebUIListenerBehavior],
 
   properties: {
     /** @type {!Array<!CupsPrinterInfo>|undefined} */
     discoveredPrinters: {
       type: Array,
     },
 
     /** @type {!CupsPrinterInfo} */
-    selectedPrinter: {
+    newPrinter: {
       type: Object,
       notify: true,
     },
 
     discovering_: {
       type: Boolean,
       value: true,
     },
   },
 
   /** @override */
   ready: function() {
     settings.CupsPrintersBrowserProxyImpl.getInstance().
         startDiscoveringPrinters();
     this.addWebUIListener('on-printer-discovered',
                           this.onPrinterDiscovered_.bind(this));
     this.addWebUIListener('on-printer-discovery-done',
                           this.onPrinterDiscoveryDone_.bind(this));
     this.addWebUIListener('on-printer-discovery-failed',
                           this.onPrinterDiscoveryDone_.bind(this));
   },
 
   /**
    * @param {!Array<!CupsPrinterInfo>} printers
    * @private
    */
   onPrinterDiscovered_: function(printers) {
-    this.discovering_ = true;
-    if (!this.discoveredPrinters) {
-      this.discoveredPrinters = printers;
-    } else {
-      for (var i = 0; i < printers.length; i++)
-        this.push('discoveredPrinters', printers[i]);
+    this.discoveredPrinters = printers;
+    if (!this.discovering_) {
+      // This update happened after we already finished the initial

[xdai1, 2017/03/31 22:08:37]

nit: comment indent off: 'scan' should be in the previous line.

[Carlson, 2017/03/31 22:58:41]

Done.

+      // scan, so re-run the discovery done logic.
+      this.onPrinterDiscoveryDone_();
     }
   },
 
   /** @private */
   onPrinterDiscoveryDone_: function() {
     this.discovering_ = false;
     this.$$('add-printer-list').style.maxHeight = kPrinterListFullHeight + 'px';
     this.$.noPrinterMessage.hidden = !!this.discoveredPrinters;
   },
 
@@ skipping 11 matching lines @@
     this.fire('open-manually-add-printer-dialog');
   },
 
   /** @private */
   onCancelTap_: function() {
     this.stopDiscoveringPrinters_();
     this.$$('add-printer-dialog').close();
   },
 
   /** @private */
   switchToConfiguringDialog_: function() {

[xdai1, 2017/03/31 22:08:38]

I think you don't need this function any more?

[Carlson, 2017/03/31 22:58:41]

Done.

     this.stopDiscoveringPrinters_();
     this.$$('add-printer-dialog').close();
     this.fire('open-configuring-printer-dialog');
   },
+
+  /** @private */
+  switchToManufacturerDialog_: function() {
+    this.stopDiscoveringPrinters_();
+    this.$$('add-printer-dialog').close();
+    this.fire('open-manufacturer-model-dialog');
+  },
 });
 
 Polymer({
   is: 'add-printer-manually-dialog',
 
   properties: {
     /** @type {!CupsPrinterInfo} */
     newPrinter: {
       type: Object,
       notify: true,
@@ skipping 182 matching lines @@
   },
 });
 
 Polymer({
   is: 'settings-cups-add-printer-dialog',
 
   behaviors: [WebUIListenerBehavior],
 
   properties: {
     /** @type {!CupsPrinterInfo} */
-    selectedPrinter: {

[xdai1, 2017/03/31 22:08:38]

Could you try to see the following scenario:

Open the discovery dialog, click and select one printer from the discovered
list, do nothing, and click on the manually add printer button, observe all the
fields. Does the printer from the discovered list influence the fields in the
manually add printer flow?

[Carlson, 2017/03/31 22:58:41]

Oh, you're good.

Yes, indeed, this is what happens, we pre-populate the manual printer fields
inappropriately, and I see why.

Clearing newPrinter on the switch from discovery to manual fixes this, and I've
done that for now, but is that the right way to do this?  I could restore the
"selected-printer" changes and copy over selectedPrinter to newPrinter on a
discovery->manufacturer transition instead.  

However, I do like keeping things as newPrinter generally as it simplified some
other things below.

Let me know which sort of fix you prefer.

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

I would prefer to restore the 'selectedPrinter' change. There are two reasons.
The first reason please refer my comment in cups_add_printer_dialog.html. The
second reason is the user may need to re-type the information he just entered
unnecessarily. Suppose the following scenario: Open the discovery dialog, then
click on manual add printer button, enter the printer information, then click on
add nearby printer button, do nothing, then click on manual add printer button
again. I would expect all the information still remains here.

But I don't have strong opinions here. If you really want to remove
selectedPrinter variable, make sure you also fix the case I described in
cups_add_printer_dialog.html.

-      type: Object,
-    },
-
-    /** @type {!CupsPrinterInfo} */
     newPrinter: {
       type: Object,
     },
 
     /** @type {boolean} whether the new printer setup is failed. */
     setupFailed: {
       type: Boolean,
       value: false,
     },
 
@@ skipping 27 matching lines @@
   },
 
   /** @override */
   ready: function() {
     this.addWebUIListener('on-add-cups-printer', this.onAddPrinter_.bind(this));
   },
 
   /** Opens the Add printer discovery dialog. */
   open: function() {
     this.resetData_();
-    this.switchDialog_(
-        '', AddPrinterDialogs.MANUALLY, 'showManuallyAddDialog_');
+    this.switchDialog_('', AddPrinterDialogs.DISCOVERY, 'showDiscoveryDialog_');
   },
 
   /**
    * Reset all the printer data in the Add printer flow.
    * @private
    */
   resetData_: function() {
-    if (this.selectedPrinter)
-      this.selectedPrinter = this.getEmptyPrinter_();
     if (this.newPrinter)
       this.newPrinter = this.getEmptyPrinter_();
     this.setupFailed = false;
   },
 
   /**
    * @return {!CupsPrinterInfo}
    * @private
    */
   getEmptyPrinter_: function() {
@@ skipping 24 matching lines @@
   },
 
   /** @private */
   openConfiguringPrinterDialog_: function() {
     this.switchDialog_(
         this.currentDialog_, AddPrinterDialogs.CONFIGURING,
         'showConfiguringDialog_');
     if (this.previousDialog_ == AddPrinterDialogs.DISCOVERY) {
       this.configuringDialogTitle =
           loadTimeData.getString('addPrintersNearbyTitle');
-      settings.CupsPrintersBrowserProxyImpl.getInstance().addCupsPrinter(
-          this.selectedPrinter);
     } else if (this.previousDialog_ == AddPrinterDialogs.MANUFACTURER) {
       this.configuringDialogTitle =
           loadTimeData.getString('addPrintersManuallyTitle');
-      settings.CupsPrintersBrowserProxyImpl.getInstance().addCupsPrinter(
-          this.newPrinter);
     }
+    settings.CupsPrintersBrowserProxyImpl.getInstance().addCupsPrinter(
+        this.newPrinter);
   },
 
   /** @private */
   openManufacturerModelDialog_: function() {
     this.switchDialog_(this.currentDialog_, AddPrinterDialogs.MANUFACTURER,
                        'showManufacturerDialog_');
   },
 
   /** @private */
   configuringDialogClosed_: function() {
@@ skipping 25 matching lines @@
         this.set(domIfBooleanName, false);
       }.bind(this));
     });
   },
 
   /**
    * @return {string} The name of the current printer in configuration.
    * @private
    */
   getConfiguringPrinterName_: function() {
-    if (this.previousDialog_ == AddPrinterDialogs.DISCOVERY)
-      return this.selectedPrinter.printerName;
-    if (this.previousDialog_ == AddPrinterDialogs.MANUALLY ||
+    if (this.previousDialog_ == AddPrinterDialogs.DISCOVERY ||
+        this.previousDialog_ == AddPrinterDialogs.MANUALLY ||
         this.previousDialog_ == AddPrinterDialogs.MANUFACTURER) {
       return this.newPrinter.printerName;
     }
     return '';
   },
 
   /**
    * @param {boolean} success
    * @param {string} printerName
    * @private
    */
   onAddPrinter_: function(success, printerName) {
     this.$$('add-printer-configuring-dialog').close();
     if (success)
       return;
 
     if (this.previousDialog_ == AddPrinterDialogs.MANUFACTURER) {
       this.setupFailed = true;
     }
   },
 });