Disable ShelfAppBrowserTest.TabDragAndDrop

Recent flake caused by suspected patch set
https://codereview.chromium.org/2696073002,
test disabled. See crbug.com/693341 for further
details.

BUG=693341
TBR=jamescook@chromium.org

Review-Url: https://codereview.chromium.org/2696133009
Cr-Commit-Position: refs/heads/master@{#451326}
1 file changed