The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/07aeedd625a49a1d7276026f545961f26690629a

commit 07aeedd625a49a1d7276026f545961f26690629a
Author: dominickn <dominickn@chromium.org>
Date: Sat Apr 30 00:32:20 2016

Add a low-frequency RAPPOR configuration, and use it for Safe Browsing and Permissions metrics.

This CL implements a new RAPPOR configuration with the F privacy
parameter set to 0.25 instead of 0.5. This has the effect of introducing
less noise into the permanent random response, and thus preserving some
additional amount of signal. The reduction has been approved by the
Privacy team for low-frequency metrics (<500,000 reports per day) and
does not compromise user's privacy or anonymity.

This CL uses the new configuration for the permissions and Safe Browsing
metrics. The existing metrics for these configurations are retained for
a comparative analysis; they will be removed entirely in a future CL.
The multi-dimensional permissions metrics are removed in this CL as they
cannot be feasibly analysed.

Any other metrics which seek to use the new low-frequency configuration
must seek approval from the Metrics and Privacy teams.

BUG= 598520 , 606645 

Review-Url: https://codereview.chromium.org/1921533004
Cr-Commit-Position: refs/heads/master@{#390819}

[modify] https://crrev.com/07aeedd625a49a1d7276026f545961f26690629a/chrome/browser/permissions/permission_uma_util.cc
[modify] https://crrev.com/07aeedd625a49a1d7276026f545961f26690629a/chrome/browser/safe_browsing/safe_browsing_blocking_page.cc
[modify] https://crrev.com/07aeedd625a49a1d7276026f545961f26690629a/chrome/browser/safe_browsing/safe_browsing_blocking_page.h
[modify] https://crrev.com/07aeedd625a49a1d7276026f545961f26690629a/chrome/browser/ssl/ssl_blocking_page.cc
[modify] https://crrev.com/07aeedd625a49a1d7276026f545961f26690629a/components/rappor/rappor_parameters.h
[modify] https://crrev.com/07aeedd625a49a1d7276026f545961f26690629a/components/security_interstitials/core/metrics_helper.cc
[modify] https://crrev.com/07aeedd625a49a1d7276026f545961f26690629a/components/security_interstitials/core/metrics_helper.h
[modify] https://crrev.com/07aeedd625a49a1d7276026f545961f26690629a/ios/chrome/browser/ssl/ios_ssl_blocking_page.mm
[modify] https://crrev.com/07aeedd625a49a1d7276026f545961f26690629a/tools/metrics/rappor/rappor.xml