linux_aura: Put toolbar dropdown menus on the screen with the cursor.

linux_aura: Put toolbar dropdown menus on the screen with the cursor.

When right clicking on, for example, the back button, the dropdown menu
should be positioned on the screen with the cursor, so that this picks
the right screen even when the back button straddles two screens,
instead of always picking the left screen.

BUG=339536
R=msw@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=250190

[msw, 2014-02-10 19:56:07]

lgtm

[Elliot Glaysher, 2014-02-10 20:18:28]

Committed patchset #1 manually as r250190 (presubmit successful).