Don't capture cursor during Pointer Lock on Windows

Pointer Lock on Windows is just accomplished by moving the mouse back to
the center of the window, but not capturing (per
RenderWidgetHostViewWin).

If capture is used, then during restoring to non-fullscreen (when having
been in fullscreen+pointerlock) the WM_SYSCOMMAND that restores the
window to maximized state is ignored by DefWindowProc.

There's a related problem that cursor clipping isn't done yet,
http://crbug.com/302025

R=ben@chromium.org
BUG=281366

Review URL: https://codereview.chromium.org/25293004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226931 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226931