Modify the windown picker dialog text to be more user-friendly.

BUG=https://code.google.com/p/webrtc/issues/detail?id=2980

Review URL: https://codereview.chromium.org/184693005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@254523 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 254523