Add UMA metrics to monitor suspicious bookmark data

We've received reports of bookmarks getting duplicated or empty titles
being padded with whitespaces. In order to investigate and rule out
regressions in ongoing launches, let's introduce some dedicated UMA.

The new code is introduced behind a feature toggle (enabled by
default).

Bug: 949571
Change-Id: I04cb3dc37a5abf6b64c591995263a9b7e69709ad
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1553546
Commit-Queue: Mikel Astiz <mastiz@chromium.org>
Reviewed-by: Brian White <bcwhite@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Marc Treib <treib@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#648476}(cherry picked from commit 32e5063c56ec9abc31bb673d765d725135c3eb81)
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1559311
Reviewed-by: Mikel Astiz <mastiz@chromium.org>
Cr-Commit-Position: refs/branch-heads/3729@{#737}
Cr-Branched-From: d4a8972e30b604f090aeda5dfff68386ae656267-refs/heads/master@{#638880}
6 files changed