Ignore mouseup shortly after showing cr.ui.Menu

This works simlarly to views::MenuController[1] by ignoring mouseups:
- less than 200ms after showing some UI
- with minimal mouse movement (4px length difference)

R=mustaq@chromium.org
BUG=531939

[1] https://goo.gl/iZht5k

Review URL: https://codereview.chromium.org/1358893003

Cr-Commit-Position: refs/heads/master@{#350323}
4 files changed