Adds Window::MoveChildToFront, with surrounding changes.

Adds Window::MoveChildToFront, with surrounding changes.

BUG=102580
102578
TEST=none
R=ben@chromium.org

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=109032

[Ben Goodger (Google), 2011-11-07 16:54:06]

lgtm

[sky, 2011-11-07 21:41:04]

My first patch didn't compile as it was trying to use EnsureRectIsVisibleInRect,
which was only in NativeWidgetWin. Turns out this code can be greatly
simplified. I removed the following:

. Passing in |Widget* other_widget| to SetBoundsConstrained. This was only used
in one place and it turns out the caller was already doing MoveAboveWidget,
which makes it unnecessary.

. Removed support for using this on child widgets. We never used this and I
don't think it really worked.

This simplification allowed me to move the function up to Widget. New patch
uploaded.

  -Scott

[Ben Goodger (Google), 2011-11-07 21:45:17]

lgtm