With this CL, SparseHistogram is usable with SparseHistogram::FactoryGet.
Next step is to implement a Histogram like macro and implement WriteHTMLGraph
and WriteAscii to have a nice output.
BUG=139612
Review URL: https://chromiumcodereview.appspot.com/12207058
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@185451 0039d316-1c4b-4281-b951-d872f2087c98