Cleanup Window::UpdateLayerName to use IntToString

Rather than snprintf.

BUG=none
TEST=none
R=ben@chromium.org

Review URL: https://codereview.chromium.org/108513010

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@240306 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 240306