Remove MessageLoop::current() usage in /content/browser/devtools

Replacing it with modern RunLoop+QuitClosure usage.

R=caseq@chromium.org

Bug: 825327
Change-Id: I43e021d3a3c5e76923e77c8d28560931dc3ee866
Reviewed-on: https://chromium-review.googlesource.com/1024445Reviewed-by: Andrey Kosyakov <caseq@chromium.org>
Commit-Queue: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#553699}

content/browser/devtools/protocol/devtools_protocol_browsertest.cc

@@ -14,7 +14,6 @@
 #include "base/json/json_reader.h"
 #include "base/json/json_writer.h"
 #include "base/logging.h"
-#include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
 #include "base/strings/stringprintf.h"
 #include "base/strings/utf_string_conversions.h"
@@ -2442,11 +2441,12 @@ class CountingDownloadFile : public download::DownloadFileImpl {
   // until data is returned.
   static int GetNumberActiveFilesFromFileThread() {
     int result = -1;
+    base::RunLoop run_loop;
     download::GetDownloadTaskRunner()->PostTaskAndReply(
         FROM_HERE,
         base::BindOnce(&CountingDownloadFile::GetNumberActiveFiles, &result),
-        base::MessageLoop::current()->QuitWhenIdleClosure());
-    base::RunLoop().Run();
+        run_loop.QuitWhenIdleClosure());
+    run_loop.Run();
     DCHECK_NE(-1, result);
     return result;
   }