Update EventSender to handle keyboard modifiers in replay events.

Original patch by erceg.david@gmail.com. This is needed to test that
holding control during a dragging operation causes it to be treated as
a copy operation instead.

BUG=49639
R=jochen@chromium.org

Review URL: https://codereview.chromium.org/179593002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@253245 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 253245