GitLab

Currently, the window for drag-drop is a normal window. This is not
right and cuases a few issues (e.g. see crbug.com/404634). This patch
changes the type to popup.

BUG=404634

Review URL: https://codereview.chromium.org/472373006

Cr-Commit-Position: refs/heads/master@{#290753}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@290753 0039d316-1c4b-4281-b951-d872f2087c98