Add onGetUsbPrinterInfoRequested event to printerProvider API.

extensions/common/api/printer_provider.idl

Index: extensions/common/api/printer_provider.idl
diff --git a/extensions/common/api/printer_provider.idl b/extensions/common/api/printer_provider.idl
index 40a07c5f5be874813d353c37288c2f70eb223c1d..3de58fa051e43423399f4895b1adb9edc637f668 100644
--- a/extensions/common/api/printer_provider.idl
+++ b/extensions/common/api/printer_provider.idl
@@ -60,6 +60,8 @@ namespace printerProvider {
 
   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>.
@@ -73,6 +75,20 @@ namespace printerProvider {
     // 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.
+    // <p><em>Note:</em> An application should not rely on this event being
+    // fired more than once per device. If a connected device is supported it
+    // should be returned in the $(ref:onGetPrintersRequested) event.</p>
+    // |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