Cleanup: Pass std::string as const reference from media/

media/capture/video/linux/video_capture_device_linux.cc

Index: media/capture/video/linux/video_capture_device_linux.cc
diff --git a/media/capture/video/linux/video_capture_device_linux.cc b/media/capture/video/linux/video_capture_device_linux.cc
index f4ca749ae9b69a6961c3ab3b41b96edd9360492d..487199ea0401cde7b438b401e10ff7ca0c5a457a 100644
--- a/media/capture/video/linux/video_capture_device_linux.cc
+++ b/media/capture/video/linux/video_capture_device_linux.cc
@@ -28,7 +28,7 @@ static const char kVidPathTemplate[] =
 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)