Add getUserSelectedDevices to the USB extensions API.

extensions/common/api/usb.idl

Index: extensions/common/api/usb.idl
diff --git a/extensions/common/api/usb.idl b/extensions/common/api/usb.idl
index af6d55054c261a7b123e729536c8fda7414e36c6..1bfc4ed9578b5769bf82398c2e513553b3bc398f 100644
--- a/extensions/common/api/usb.idl
+++ b/extensions/common/api/usb.idl
@@ -186,7 +186,7 @@ namespace usb {
     // will return all devices the app has permission for.
     DeviceFilter[]? filters;
   };
-  
+
   dictionary EnumerateDevicesAndRequestAccessOptions {
     // The device vendor ID.
     long vendorId;
@@ -197,6 +197,14 @@ namespace usb {
     long? interfaceId;
   };
 
+  dictionary DevicePromptOptions {
+    // Allow the user to select multiple devices.
+    boolean? multiple;
+    // Filter the list of devices presented to the user. If multiple filters are
+    // provided devices matching any filter will be displayed.
+    DeviceFilter[]? filters;
+  };
+
   callback VoidCallback = void ();
   callback GetDevicesCallback = void (Device[] devices);
   callback RequestAccessCallback = void (boolean success);
@@ -214,6 +222,16 @@ namespace usb {
     static void getDevices(EnumerateDevicesOptions options,
                            GetDevicesCallback callback);
 
+    // Presents a device picker to the user and returns the $(ref:Device)s
+    // selected.
+    // If the user cancels the picker devices will be empty. A user gesture
+    // is required for the dialog to display. Without a user gesture, the
+    // callback will run as though the user cancelled.
+    // |options|: Configuration of the device picker dialog box.
+    // |callback|: Invoked with a list of chosen $(ref:Device)s.
+    static void getUserSelectedDevices(DevicePromptOptions options,
+                                       GetDevicesCallback callback);
+
     // Requests access from the permission broker to a device claimed by
     // ChromeOS if the given interface on the device is not claimed.
     //