implementation for new duplicate download UI

This change implements the new duplicate download UI.
It renames the DownloadOverwriteInfobarXXXX to DuplicateDownloadInfobarXXXX.
Chrome no longer show the overwrite button,
and always creating a new file if user click on the download button.

BUG=658239

Review-Url: https://codereview.chromium.org/2478583004
Cr-Commit-Position: refs/heads/master@{#431389}
33 files changed