Support saving browser metrics to disk and reading them
during next run.

This CL doesn't attempt to persist metrics during a
crash.  That will be addressed later.

BUG=546019
TBR=nasko
nasko: browser_main_runner.cc (moved existing creation code earlier but disable it until experiment is examined)

Review-Url: https://codereview.chromium.org/1891913002
Cr-Commit-Position: refs/heads/master@{#393521}


CrOS-Libchrome-Original-Commit: 65e57d078b22b3695af734e0262c2b076a21b428
12 files changed
tree: 11d38a8200566eb321854abbde96137c71af6068
  1. base/
  2. build/
  3. components/
  4. dbus/
  5. device/
  6. ipc/
  7. mojo/
  8. testing/
  9. third_party/
  10. ui/