Fix UMA metric "WinJumplist.DirectoryStatusJumpListIconsOld"

The base::IsDirectoryEmpty() method returns true when the directory
doesn't exist or the directory is empty. We need to use
base::DirectoryExists() together with base::IsDirectoryEmpty() to
differentiate these two situations.

BUG=40407, 179576

Review-Url: https://codereview.chromium.org/2806873002
Cr-Commit-Position: refs/heads/master@{#463297}
1 file changed