CrOS - about:discards shows tab to discard in OOM situations

Added a simple, non-localized debug page to show the output of
the OOM-adjust algorithm, in preparation for discarding a tab in
low memory situations.  See "Out of memory handling" Chrome OS
design doc for details.

BUG=chromium-os:18375
TEST=open 3 tabs and navigate to web pages, wait 10 seconds, then open a tab to "about:discards".  It should list 3 tabs and itself.  Order is unimportant for now.

Review URL: http://codereview.chromium.org/7754002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@100170 0039d316-1c4b-4281-b951-d872f2087c98
6 files changed