Added BackgroundContentsService to manage lifecycle of BackgroundContents.
If --restore-background-contents flag is passed, stores the URLs of running
BackgroundContents in preferences so they can be re-launched when the browser
restarts.
Moved logic to shutdown background contents into BackgroundContentsService so
we can use this to coordinate when to keep the browser process running.
BUG=43382
TEST=new tests
Review URL: http://codereview.chromium.org/2104018
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@50329 0039d316-1c4b-4281-b951-d872f2087c98
23 files changed
