Safeguard histogram accesses against null pointers. This can happen when various tasks run as the static destructors for histograms are concurrently running.
Safeguard histogram accesses against null pointers.
This can happen when various tasks run as the static destructors
for histograms are concurrently running.

BUG=none
TEST=none

Review URL: http://codereview.chromium.org/2873009

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@50478 0039d316-1c4b-4281-b951-d872f2087c98

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