Avoid using !OS() constructs. Simplify guards to take advantage of the facts that !OS(POSIX) means OS(WIN).

Also fix a bug spotted for OS(ANDROID). Make OS(ANDROID) behave the same way as OS(WIN) and OS(MACOSX) inside EventHandler::shouldTurnVerticalTicksIntoHorizontal().

Review URL: https://chromiumcodereview.appspot.com/23654015

git-svn-id: svn://svn.chromium.org/blink/trunk@157500 bbb929c8-8fbe-4397-9dbb-9b2b20218538