DictionaryValue: add standard iterators

This allows dictionary values to be efficiently moved out of the
dictionary during iteration, allowing us to implement e.g. a
faster MergeDictionary.

Bug: 
Change-Id: I7580d2664568f5c3fb465f7d65926e3f36243f0d
Reviewed-on: https://chromium-review.googlesource.com/505892
Commit-Queue: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Johan Tibell <tibell@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#472731}

CrOS-Libchrome-Original-Commit: 71bba86c8ae73b633acc45bd80fa8e3cecd02f00
2 files changed
tree: b9451759866dc76d09b96181eb3c7a49243134b4
  1. base/
  2. build/
  3. components/
  4. dbus/
  5. device/
  6. ipc/
  7. mojo/
  8. testing/
  9. third_party/
  10. ui/