Merge 166715 - Revert r165772: Keep browser process alive while there are platform apps with backgr…

Merge 166715 - Revert r165772: Keep browser process alive while there are platform apps with background pages running.

Change r165772 broke logout on official Chrome OS, such that Chrome
crashes every time you log out. This was caught by our bots which
immediately started failing every time, starting with r165772.

I tested this change on Chrome OS bots and confirmed that the
Chrome OS bots were fixed.

TBR=benwells@chromium.org
BUG=chromium:155457, chromium-os:36058
TEST=Run Chrome and Chrome OS trybots on several architectures. Verify
Chrome OS build is reliable now and that all Chrome browser tests still
pass.

Original CL description:

This change prevents platform apps getting killed unceremoniously
while they have background pages active.

This also delays the process being shutdown after closing the last platform
app window, as background pages are kept alive for 15 seconds after their
last activity is completed.
Review URL: https://codereview.chromium.org/11275209

TBR=davidjames@google.com
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=166735

[benwells, 2012-11-09 08:45:22]

lgtm