Prepare for switching to libziparchive.

Bug: 19765860
Change-Id: I58249d28fbc4975428d0dcac5107d1994c35676c
diff --git a/fastboot/usb.h b/fastboot/usb.h
index 17cf0a9..c7b748e 100644
--- a/fastboot/usb.h
+++ b/fastboot/usb.h
@@ -29,6 +29,10 @@
 #ifndef _USB_H_
 #define _USB_H_
 
+#if defined(__cplusplus)
+extern "C" {
+#endif
+
 typedef struct usb_handle usb_handle;
 
 typedef struct usb_ifc_info usb_ifc_info;
@@ -64,4 +68,8 @@
 int usb_write(usb_handle *h, const void *_data, int len);
 int usb_wait_for_disconnect(usb_handle *h);
 
+#if defined(__cplusplus)
+}
+#endif
+
 #endif