Update USB extension API with suggestions from review.

chrome/browser/extensions/api/usb/usb_api.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_BROWSER_EXTENSIONS_API_USB_USB_API_H_
 #define CHROME_BROWSER_EXTENSIONS_API_USB_USB_API_H_
 
 #include <string>
 
 #include "base/memory/ref_counted.h"
@@ skipping 26 matching lines @@
   void CompleteWithError(const std::string& error);
 
   ApiResourceManager<UsbDeviceResource>* manager_;
 };
 
 class UsbAsyncApiTransferFunction : public UsbAsyncApiFunction {
  protected:
   UsbAsyncApiTransferFunction();
   virtual ~UsbAsyncApiTransferFunction();
 
-  bool ConvertDirectionSafely(const std::string& input,
+  bool ConvertDirectionSafely(const extensions::api::usb::Direction& input,
                               UsbDevice::TransferDirection* output);
-  bool ConvertRequestTypeSafely(const std::string& input,
+  bool ConvertRequestTypeSafely(const extensions::api::usb::RequestType& input,
                                 UsbDevice::TransferRequestType* output);
-  bool ConvertRecipientSafely(const std::string& input,
+  bool ConvertRecipientSafely(const extensions::api::usb::Recipient& input,
                               UsbDevice::TransferRecipient* output);
 
   void OnCompleted(UsbTransferStatus status,
                    scoped_refptr<net::IOBuffer> data,
                    size_t length);
 };
 
 class UsbFindDevicesFunction : public UsbAsyncApiFunction {
  public:
   DECLARE_EXTENSION_FUNCTION_NAME("usb.findDevices");
@@ skipping 145 matching lines @@
   virtual bool Prepare() OVERRIDE;
   virtual void AsyncWorkStart() OVERRIDE;
 
  private:
   scoped_ptr<extensions::api::usb::IsochronousTransfer::Params> parameters_;
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_API_USB_USB_API_H_