DevTools: Display a warning when trying to open untrusted frontend.

When Chrome is trying to inspect a page on a connected Android device the DevTools frontend is fetched from a URL supplied by the remote browser.
Currently Chrome would crash if this URL is not pointing to a trusted source. For instance, this happens when trying to inspect a page in ContentShell.

This patch removes the CHECKs and displays a text warning instead.

BUG=295979

Review URL: https://codereview.chromium.org/27693002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@229371 0039d316-1c4b-4281-b951-d872f2087c98
Move out all supervised user related code to separate class.

BUG=244472
TBR=bauerb@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/27700004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@229372 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 229372
Remove PrerenderRenderViewHostObserver.

It's only used to listen for a print message that we can listen for via
WebContentsObserver. (And if we ever decide to extend prerender to handle
multiple RVHs, this is probably a worthwhile change.)

BUG=none
TEST=PrerenderBrowserTest.PrerenderPrint

Review URL: https://codereview.chromium.org/27705004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@229373 0039d316-1c4b-4281-b951-d872f2087c98
Copy the children list while hiding windows as it changes on hide.

BUG=306277
TEST=WindowSelectorTest.CyclePanelVisibility

Review URL: https://codereview.chromium.org/27706002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@229374 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 229374