maximumAge and timeout should be used after initialization.

Local variables(maximumAge and timeout) in PositionOptions constructor
could be used without initializing, if "options.get()" returns false.

BUG=390314

Review URL: https://codereview.chromium.org/382443002

git-svn-id: svn://svn.chromium.org/blink/trunk@177789 bbb929c8-8fbe-4397-9dbb-9b2b20218538