Note: the original issue for implementing this was  issue 461671 .

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/d483ee26411adad910ca8e3bfa2ac16e2831eba0

commit d483ee26411adad910ca8e3bfa2ac16e2831eba0
Author: Takayoshi Kochi <kochi@chromium.org>
Date: Mon Jul 09 11:25:40 2018

Remove RAPPOR stat collecting code

This CL removes RAPPOR stat collecting code for Shadow DOM V0
and Custom Elements V0, as we are now using UKM instead.

Bug:  855343 
Change-Id: Ic05b2d5da5c20b8fe6d0e02a34f3901344a4697d
Reviewed-on: https://chromium-review.googlesource.com/1127759
Reviewed-by: Robert Kaplow <rkaplow@chromium.org>
Reviewed-by: Hayato Ito <hayato@chromium.org>
Commit-Queue: Takayoshi Kochi <kochi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#573269}
[modify] https://crrev.com/d483ee26411adad910ca8e3bfa2ac16e2831eba0/third_party/blink/renderer/core/dom/document.cc
[modify] https://crrev.com/d483ee26411adad910ca8e3bfa2ac16e2831eba0/third_party/blink/renderer/core/dom/element.cc
[modify] https://crrev.com/d483ee26411adad910ca8e3bfa2ac16e2831eba0/third_party/blink/renderer/core/dom/element.h
[modify] https://crrev.com/d483ee26411adad910ca8e3bfa2ac16e2831eba0/third_party/blink/renderer/core/dom/element.idl
[modify] https://crrev.com/d483ee26411adad910ca8e3bfa2ac16e2831eba0/tools/metrics/rappor/rappor.xml