Linux: Fix about:memory for SUID sandbox + pid namespaces.
Linux: Fix about:memory for SUID sandbox + pid namespaces.

BUG=36934
TEST=about:memory works on Linux machines with pid namespaces enabled.
Review URL: http://codereview.chromium.org/752001

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@41075 0039d316-1c4b-4281-b951-d872f2087c98

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