Add onGetUsbPrinterInfoRequested event to printerProvider API.

chrome/browser/ui/webui/print_preview/extension_printer_handler.h

Index: chrome/browser/ui/webui/print_preview/extension_printer_handler.h
diff --git a/chrome/browser/ui/webui/print_preview/extension_printer_handler.h b/chrome/browser/ui/webui/print_preview/extension_printer_handler.h
index 9995184afd6a0b8c6d794aa1721b2c9b3fa96feb..b4be2341c0a105abbd5848fdbbb8f57c2ab5dc35 100644
--- a/chrome/browser/ui/webui/print_preview/extension_printer_handler.h
+++ b/chrome/browser/ui/webui/print_preview/extension_printer_handler.h
@@ -41,6 +41,8 @@ class PWGRasterConverter;
 // extension API.
 class ExtensionPrinterHandler : public PrinterHandler {
  public:
+  using GrantUsbPrinterAccessCallback =
+      base::Callback<void(const base::DictionaryValue& printer_info)>;
   using PrintJobCallback =
       base::Callback<void(scoped_ptr<extensions::PrinterProviderPrintJob>)>;
 
@@ -66,6 +68,11 @@ class ExtensionPrinterHandler : public PrinterHandler {
                   const scoped_refptr<base::RefCountedMemory>& print_data,
                   const PrinterHandler::PrintCallback& callback) override;
 
+  void StartGrantUsbPrinterAccess(
+      const std::string& extension_id,
+      int device_id,
+      const GrantUsbPrinterAccessCallback& callback);
+
  private:
   friend class ExtensionPrinterHandlerTest;
 
@@ -102,6 +109,9 @@ class ExtensionPrinterHandler : public PrinterHandler {
   void WrapPrintCallback(const PrinterHandler::PrintCallback& callback,
                          bool success,
                          const std::string& status);
+  void WrapGrantUsbPrinterAccessCallback(
+      const GrantUsbPrinterAccessCallback& callback,
+      const base::DictionaryValue& printer_info);
 
   content::BrowserContext* browser_context_;