Linux: avoid browser windows moving around by the size of WM decorations over restart.

Use a debounce timer to get the true window position shortly after the last reconfigure event is delivered, and save that.
BUG=18771
TEST=none

Review URL: http://codereview.chromium.org/203027

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@26617 0039d316-1c4b-4281-b951-d872f2087c98