Undo of delete/forward-delete of a word should not select the deleted word on non-mac platforms

Currently on deleting a word(character granularity or by ctrl+backspace)
and undoing it,the deleted word gets selected.
Instead it should not be selected and the caret should be placed at the
position from where the deletion was actually started.
This patch introduces this behavior change for non-mac platforms.

This is achieved by not setting a new starting selection after every
delete.

This aligns chrome behavior with that of IE and FF wrt selection of
deleted words.

R=ojan, yosin

Review URL: https://codereview.chromium.org/43143003

git-svn-id: svn://svn.chromium.org/blink/trunk@160868 bbb929c8-8fbe-4397-9dbb-9b2b20218538