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This code exhibits addressability bugs under valgrind:
http://build.chromium.org/p/chromium.memory.fyi/builders/Linux%20Tests%20%28valgrind%29%281%29/builds/26205

Please investigate and reland with a clean valgrind trybot run.

> Add a HistogramRecorder class and use cases.
> 
> This CL adds a utility class to streamline the task of testing that metrics have been updated as expected. Specifically, the HistogramRecorder class allows a client to obtain the differential value of a given histogram in the interval since the given HistogramRecorder instance was created.
> 
> BUG=232414
> 
> Review URL: https://chromiumcodereview.appspot.com/18337014

TBR=lpromero@chromium.org

Review URL: https://codereview.chromium.org/19722009

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@212419 0039d316-1c4b-4281-b951-d872f2087c98