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..02409eceaaca16558d966e153e1a26494b226cc8 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 +75,17 @@ 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.

[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