Trying again to land OOM priority manager changes.

First landing failed because of an obscure problem with building
linux_shared. This change passes the linux_shared trybot (and
linux and linux_chromeos trybots).

Changing OOM range to 0, 1000 and tweaking OOM algorithm.

With this change, we now use the newer oom_score_adj file (with
fallback to oom_adj when on a system that doesn't support it) so that
we can take advantage of a finer range ([0, 1000] instead of [0, 15]).

Also tweaked the OOM priority manager to prioritize things in a
slightly different order, preferring (even more) not to kill tabs that
the user has currently selected.

Original review: http://codereview.chromium.org/7671033/

BUG=chromium-os:18421, chromium:65009
TEST=Ran on device, observed OOM adj values, forced OOM conditions to
watch kills.

Review URL: http://codereview.chromium.org/7708020

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@97888 0039d316-1c4b-4281-b951-d872f2087c98

• base/process_util.cc[diff]
• base/process_util.h[diff]
• base/process_util_linux.cc[diff]
• chrome/app/chrome_main.cc[diff]
• chrome/browser/oom_priority_manager.cc[diff]
• chrome/browser/oom_priority_manager.h[diff]
• chrome/browser/ui/browser_list.h[diff]
• chrome/common/chrome_constants.cc[diff]
• chrome/common/chrome_constants.h[diff]
• content/browser/zygote_host_linux.cc[diff]
• content/browser/zygote_host_linux.h[diff]
• sandbox/linux/suid/process_util.h[diff]
• sandbox/linux/suid/process_util_linux.c[diff]
• sandbox/linux/suid/sandbox.c[diff]