Chrome allows WebTouchPoint to store WebFloatPoint instead of WebPoint (part 2)

The previous patch (https://codereview.chromium.org/140973005/) missed some
necessary changes in some tests.

This introduces some temporary casts to WebPoint in chromium, to allow
a blink modification to store WebFloatPoint in WebTouchPoint
(https://codereview.chromium.org/149053002/). These changes will be
cleaned up once the blink patch has landed.

BUG=336807

Review URL: https://codereview.chromium.org/138003014

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@248225 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 248225