Dispatch middle click manually by tracking mouse

Tracking targets for middle button mousedown event
and fire click event for it on mouse up if necessary.

Note: The click is not finding the common parent of
mousedown and up targets for simplicty and only sends
the click to the target if both down and up happened
on the same node.

BUG=608697
CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/1963823002
Cr-Commit-Position: refs/heads/master@{#395707}
2 files changed