Add the user metrics to EditorCommand

Add the UMA histogram metrics counting each executed command as autogenerated ID.
We will add a histogram declaration to chrome/trunk/src/tools/metrics/histograms/histograms.xml in another CL.
BUG=338241

Review URL: https://codereview.chromium.org/148083003

git-svn-id: svn://svn.chromium.org/blink/trunk@165849 bbb929c8-8fbe-4397-9dbb-9b2b20218538