Add onGetUsbPrinterInfoRequested event to printerProvider API.

extensions/common/api/printer_provider.idl

 // Copyright 2014 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.
 
 // The <code>chrome.printerProvider</code> API exposes events used by print
 // manager to query printers controlled by extensions, to query their
 // capabilities and to submit print jobs to these printers.
 namespace printerProvider {
   // Error codes returned in response to $(ref:onPrintRequested) event.
   enum PrintError {
@@ skipping 42 matching lines @@
     // <code>"application/pdf"</code> and <code>"image/pwg-raster"</code>.
     DOMString contentType;
 
     // Blob containing the document data to print. Format must match
     // |contentType|.
     [instanceOf=Blob] object document;
   };
 
   callback PrintersCallback = void(PrinterInfo[] printerInfo);
 
+  callback PrinterInfoCallback = void(optional PrinterInfo printerInfo);
+
   // |capabilities|: Device capabilities in
   // <a href="https://developers.google.com/cloud-print/docs/cdd#cdd">CDD
   // format</a>.
   callback CapabilitiesCallback = void(object capabilities);
 
   callback PrintCallback = void(PrintError result);
 
   interface Events {
     // Event fired when print manager requests printers provided by extensions.
     // |resultCallback|: Callback to return printer list. Every listener must
     // call callback exactly once.
     static void onGetPrintersRequested(PrintersCallback resultCallback);
 
+    // Event fired when print manager requests information about a USB device
+    // that may be a printer.

[tbarzic, 2015/05/28 22:20:50]

Add a note that the extension should not rely on this event being fired more
than once per device (and, if the device is supported, should include this
printer in the list returned by onGetPrintersRequested)

[Reilly Grant (use Gerrit), 2015/05/28 22:38:58]

Done.

+    // |device|: The USB device.
+    // |resultCallback|: Callback to return printer info. The receiving listener
+    // must call callback exactly once. If the parameter to this callback is
+    // undefined that indicates that the application has determined that the
+    // device is not supported.
+    static void onGetUsbPrinterInfoRequested(
+        usb.Device device,
+        PrinterInfoCallback resultCallback);
+
     // Event fired when print manager requests printer capabilities.
     // |printerId|: Unique ID of the printer whose capabilities are requested.
     // |resultCallback|: Callback to return device capabilities in
     // <a href="https://developers.google.com/cloud-print/docs/cdd#cdd">CDD
     // format</a>.
     // The receiving listener must call callback exectly once.
     static void onGetCapabilityRequested(DOMString printerId,
                                          CapabilitiesCallback resultCallback);
 
     // Event fired when print manager requests printing.
     // |printJob|: The printing request parameters.
     // |resultCallback|: Callback that should be called when the printing
     // request is completed.
     static void onPrintRequested(PrintJob printJob,
                                  PrintCallback resultCallback);
   };
 };