Report shared dirty in memory metrics.

In addition to PSS and private dirty, shared dirty is also a useful
metric to understand RAM usage.

BUG=303194

Review URL: https://codereview.chromium.org/25892004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@227414 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 227414
Valgrind: Remove the exclusion entry for a non-existent test.

BUG=247440
NOTRY=true
TBR=dewittj@chromium.org

Review URL: https://codereview.chromium.org/26418003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@227415 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 227415