fuchsia: Implement rand_util

There's no /dev/urandom on Fuchsia, but mx_cprng_draw() is similar to
base::RandBytes().

Ref: https://fuchsia.googlesource.com/magenta/+/HEAD/docs/syscalls/cprng_draw.md

Makes RandUtilTest.* pass.

Bug: 706592
Change-Id: Idd16d322b965be498d733aa29a2d7764145408d7
Reviewed-on: https://chromium-review.googlesource.com/520607
Commit-Queue: Scott Graham <scottmg@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#476410}

CrOS-Libchrome-Original-Commit: 4ffd63b5892e5a92f7fecb1a873883f406bb8033
2 files changed
tree: 50e22e92a9c85bf9846092db5101247c377d06d4
  1. base/
  2. build/
  3. components/
  4. dbus/
  5. device/
  6. ipc/
  7. mojo/
  8. testing/
  9. third_party/
  10. ui/