Make DOMWindow methods use the same rounding for zoom as elsewhere

Use adjustForAbsoluteZoom and get rid of the mapping methods in
FrameView which are only used by DOMWindow.

Test added: LayoutTests/fast/media/mq-width-on-zoom.html

Review URL: https://codereview.chromium.org/102283002

git-svn-id: svn://svn.chromium.org/blink/trunk@163126 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Move Theme.cpp/.h to platform/

BUG=297477

Review URL: https://codereview.chromium.org/102453003

git-svn-id: svn://svn.chromium.org/blink/trunk@163127 bbb929c8-8fbe-4397-9dbb-9b2b20218538