Expose registered histograms from FeedbackCollector

The registered histograms on the native side are exposed
as JSON text from the FeedbackCollector. The histograms are
exposed only if:
(i)  "Include screenshot and logs" is checked when
the feedback was collected, and
(ii) The feedback is submitted from a non-incognito
profile.

In the next CL, these would be attached to the feedback
report.

BUG=651621

Review-Url: https://codereview.chromium.org/2378773010
Cr-Commit-Position: refs/heads/master@{#422765}


CrOS-Libchrome-Original-Commit: 80c5d05018d8c2ef7a95421e971166175870d050
4 files changed
tree: d7be31dcc0e1aa3c612d3d2dca8ec9651fde13a2
  1. base/
  2. build/
  3. components/
  4. dbus/
  5. device/
  6. ipc/
  7. mojo/
  8. testing/
  9. third_party/
  10. ui/