Add a unit test that filenames aren't unintentionally converted to URLs.

Also fixes two issues in OSExchangeDataProviderWin:
- It used a disjoint set of clipboard formats when handling
  GetUrl(..., true /* filename conversion */) vs GetFilenames(...), so the
  actual returned results would vary depending on which one was called.
- It incorrectly used ::DragFinish() instead of ::ReleaseStgMedium().
  ::DragFinish() is only meant to be used in conjunction with WM_DROPFILES.

BUG=346135

Review URL: https://codereview.chromium.org/380553002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@283226 0039d316-1c4b-4281-b951-d872f2087c98
void OSExchangeDataProviderWin::SetDownloadFileInfo(
    const OSExchangeData::DownloadFileInfo& download) {
  STGMEDIUM* storage = NULL;
  if (!download.filename.empty())
    storage = GetStorageForFileName(download.filename);

  DataObjectImpl::StoredDataInfo* info = new DataObjectImpl::StoredDataInfo(
      Clipboard::GetCFHDropFormatType().ToFormatEtc(), storage);
  info->downloader = download.downloader;
  data_->contents_.push_back(info);
}

void OSExchangeDataProviderWin::SetDownloadFileInfo(
    const OSExchangeData::DownloadFileInfo& download) {
  STGMEDIUM* storage = NULL;
  if (!download.filename.empty())
    storage = GetStorageForFileName(download.filename);

  DataObjectImpl::StoredDataInfo* info = new DataObjectImpl::StoredDataInfo(
      Clipboard::GetCFHDropFormatType().ToFormatEtc(), storage);
  info->downloader = download.downloader;
  data_->contents_.push_back(info);
}
