Attempt 3 at: Makes tab dragging code set bounds before creating window, that way

Attempt 3 at: Makes tab dragging code set bounds before creating window, that way
window sizer doesn't kick in and have side effects.

This is the same as the first version. I reverted the last (second
version) since the waterfall was happy and I need a clean version to
merge over.

TBR since same as first.

BUG=150868
TEST=create a single window with two tabs. Drag tab out and make sure
     windows don't change position. Also covered by tests now.
R=skuhne@chromium.org
TBR=skuhne@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=158611