Correcting menu button event trigger location

BUG=64415

Review URL: https://codereview.chromium.org/247023002

git-svn-id: svn://svn.chromium.org/blink/trunk@172336 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Add TreeScope::commonAncestorTreeScope().

It turned out that it would be nice to have the functionality to calculate
the lowest common ancestor of tree scopes while I was trying to fix issue
365246.

This patch adds the titled function to TreeScope along with some unit tests.

BUG=365246

Review URL: https://codereview.chromium.org/244263005

git-svn-id: svn://svn.chromium.org/blink/trunk@172337 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Remove one more async step in test.

BUG=306228
TBR=vsevik

Review URL: https://codereview.chromium.org/246883008

git-svn-id: svn://svn.chromium.org/blink/trunk@172338 bbb929c8-8fbe-4397-9dbb-9b2b20218538