Consider follow up and use actual bucket count when storing samples.
BUG=
Review-Url: https://codereview.webrtc.org/2008483002
Cr-Commit-Position: refs/heads/master@{#12872}
Updated tests to use the default implementation and removed the test implementation (webrtc/test/histograms.h).
BUG=
Review-Url: https://codereview.webrtc.org/1915523002
Cr-Commit-Position: refs/heads/master@{#12829}