Merge multiple histogram snapshots into single one for reporting.

With multiple processes each now capable of reporting seperately,
the values need to be merged before being flattened and sent
to the server in order to conserve server space.

BUG=546019

Review URL: https://codereview.chromium.org/1485763002

Cr-Commit-Position: refs/heads/master@{#376264}


CrOS-Libchrome-Original-Commit: c85a1f82ce2ab8c4ff9c19989f17234ea8abb865
11 files changed
tree: f6784afbb4f5fa7141e96c134a414483b60a8bf3
  1. base/
  2. build/
  3. components/
  4. dbus/
  5. device/
  6. ipc/
  7. mojo/
  8. testing/
  9. third_party/
  10. ui/