Fix trace parameter showing gibberish.

content/browser/download/mhtml_generation_manager.cc

Index: content/browser/download/mhtml_generation_manager.cc
diff --git a/content/browser/download/mhtml_generation_manager.cc b/content/browser/download/mhtml_generation_manager.cc
index 1e8b0549fd35007c849f387da6435a114ffbb594..83567840b2196739e8a40e3b61af396f1555a1b2 100644
--- a/content/browser/download/mhtml_generation_manager.cc
+++ b/content/browser/download/mhtml_generation_manager.cc
@@ -394,8 +394,8 @@ void MHTMLGenerationManager::SaveMHTML(WebContents* web_contents,
   Job* job = NewJob(web_contents, params, callback);
   TRACE_EVENT_NESTABLE_ASYNC_BEGIN2(
       "page-serialization", "SavingMhtmlJob", job, "url",
-      web_contents->GetLastCommittedURL().possibly_invalid_spec().c_str(),
-      "file", params.file_path.value().c_str());
+      web_contents->GetLastCommittedURL().possibly_invalid_spec(),
+      "file", params.file_path.AsUTF8Unsafe());
 
   BrowserThread::PostTaskAndReplyWithResult(
       BrowserThread::FILE, FROM_HERE,