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

chrome/browser/tracing/crash_service_uploader.cc

Index: chrome/browser/tracing/crash_service_uploader.cc
diff --git a/chrome/browser/tracing/crash_service_uploader.cc b/chrome/browser/tracing/crash_service_uploader.cc
index caa266eaaa10f4ae33d017a11dbb0d2886f97da8..b987e89c67dbd6d88a833ee8469706fc0921e36c 100644
--- a/chrome/browser/tracing/crash_service_uploader.cc
+++ b/chrome/browser/tracing/crash_service_uploader.cc
@@ -194,7 +194,8 @@ void TraceCrashServiceUploader::DoUploadOnFileThread(
                  base::Unretained(this), upload_url, post_data));
 }
 
-void TraceCrashServiceUploader::OnUploadError(std::string error_message) {
+void TraceCrashServiceUploader::OnUploadError(
+    const std::string& error_message) {
   LOG(ERROR) << error_message;
   content::BrowserThread::PostTask(
       content::BrowserThread::UI, FROM_HERE,