Update UI for extension destinations in print preview destination list

extensions/browser/api/printer_provider/printer_provider_api.h

Index: extensions/browser/api/printer_provider/printer_provider_api.h
diff --git a/extensions/browser/api/printer_provider/printer_provider_api.h b/extensions/browser/api/printer_provider/printer_provider_api.h
index c2317d1cf14fe634693e45025d20fdbd74ea27a0..0926a6b86d0781cbf4846b8965638d55c9efc50d 100644
--- a/extensions/browser/api/printer_provider/printer_provider_api.h
+++ b/extensions/browser/api/printer_provider/printer_provider_api.h
@@ -47,6 +47,17 @@ class PrinterProviderAPI : public KeyedService {
 
   ~PrinterProviderAPI() override {}
 
+  // Requests list of supported printers from extensions implementing
+  // chrome.printerProvider API. It dispatches
+  // chrome.printerProvider.onGetPrintersRequested event. The callback is
+  // called once for every extension handling the event with a list of its
+  // supported printers. The printer values reported by an extension are
+  // added "extensionId" property that is set to the ID of the extension
+  // returning the list and "extensionName" property set to the extension's
+  // name.
+  // Note that the "id" property of printer values reported by an extension are
+  // rewriten as "<extension_id>:<id>" to ensure they are unique across
+  // different extensions.
   virtual void DispatchGetPrintersRequested(
       const GetPrintersCallback& callback) = 0;