Add a manifest property declaring USB printers supported by an app.

extensions/common/api/printer_provider/usb_printer_manifest_handler.h

+// Copyright 2015 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 EXTENSIONS_COMMON_API_PRINTER_PROVIDER_USB_PRINTER_MANIFEST_HANDLER_H_
+#define EXTENSIONS_COMMON_API_PRINTER_PROVIDER_USB_PRINTER_MANIFEST_HANDLER_H_
+
+#include "extensions/common/manifest_handler.h"
+
+namespace extensions {
+
+// Parses the "usb_printers" manifest key.
+class UsbPrinterManifestHandler : public ManifestHandler {
+ public:
+  UsbPrinterManifestHandler();
+  ~UsbPrinterManifestHandler() override;
+
+ private:
+  // ManifestHandler overrides.
+  bool Parse(Extension* extension, base::string16* error) override;
+  const std::vector<std::string> Keys() const override;
+};
+
+}  // namespace extensions
+
+#endif  // EXTENSIONS_COMMON_API_PRINTER_PROVIDER_USB_PRINTER_MANIFEST_HANDLER_H_