Fix cursor regression introduced in r171859.

We actually used to change cursor when page is inactive, even though
FrameView::shouldSetCursor returns false.
Changed FrameView::setCursor to only check for mouse support.

BUG=337142

Review URL: https://codereview.chromium.org/243073002

git-svn-id: svn://svn.chromium.org/blink/trunk@171950 bbb929c8-8fbe-4397-9dbb-9b2b20218538