Chromium Rule: ScopedTempDir should always be destroyed last

Many tear-down can occur if this is not the case: bug references can be
for the curious.

Tbr: slangley, yamaguchi
No-Presubmit: true
Bug: 833834
Change-Id: I5e795f7ef5b5e28af4050c9506640d8f6df8941a
Reviewed-on: https://chromium-review.googlesource.com/1038983Reviewed-by: Noel Gordon <noel@chromium.org>
Commit-Queue: Noel Gordon <noel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#555284}

chrome/browser/chromeos/file_manager/file_manager_browsertest_base.cc

@@ -258,9 +258,9 @@ class TestVolume {
   }
 
  private:
-  std::string name_;
   base::ScopedTempDir root_;
   bool root_initialized_ = false;
+  std::string name_;
 };
 
 }  // anonymous namespace