This adds a "killed tab" page to be displayed in the case where a tab is killed instead of crashing.

It also adds "about:kill" to simulate kills.

On ChromeOS killed tabs will be reloaded as soon as the user clicks on them unless they are the only tab, or the currently focused tab is killed.

BUG=http://crosbug.com/10043, http://crosbug.com/10711
TEST=Built linux and ChromeOS Chrome and killed a tab, and then did about:crash and made sure that the "Aw, Snap!" page was displayed. Did about:kill and made sure kill page was displayed.

Review URL: http://codereview.chromium.org/6053012

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@71360 0039d316-1c4b-4281-b951-d872f2087c98