Cleanup: Pass std::string as const reference if possible

media/capture/video/linux/video_capture_device_linux.cc

 // 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.
 
 #include "media/capture/video/linux/video_capture_device_linux.h"
 
 #if defined(OS_OPENBSD)
 #include <sys/videoio.h>
 #else
 #include <linux/videodev2.h>
@@ skipping 10 matching lines @@
 // USB VID and PID are both 4 bytes long.
 static const size_t kVidPidSize = 4;
 
 // /sys/class/video4linux/video{N}/device is a symlink to the corresponding
 // USB device info directory.
 static const char kVidPathTemplate[] =
     "/sys/class/video4linux/%s/device/../idVendor";
 static const char kPidPathTemplate[] =
     "/sys/class/video4linux/%s/device/../idProduct";
 
-static bool ReadIdFile(const std::string path, std::string* id) {
+static bool ReadIdFile(const std::string& path, std::string* id) {
   char id_buf[kVidPidSize];
   FILE* file = fopen(path.c_str(), "rb");
   if (!file)
     return false;
   const bool success = fread(id_buf, kVidPidSize, 1, file) == 1;
   fclose(file);
   if (!success)
     return false;
   id->append(id_buf, kVidPidSize);
   return true;
@@ skipping 96 matching lines @@
       return V4L2_CID_POWER_LINE_FREQUENCY_50HZ;
     case static_cast<int>(media::PowerLineFrequency::FREQUENCY_60HZ):
       return V4L2_CID_POWER_LINE_FREQUENCY_60HZ;
     default:
       // If we have no idea of the frequency, at least try and set it to AUTO.
       return V4L2_CID_POWER_LINE_FREQUENCY_AUTO;
   }
 }
 
 }  // namespace media