Move String16 mojom to mojo/public/cpp/base

Also, for filenames related to String16, struct_traits => mojom_traits
and CommonCustomTypesStructTraits => String16MojomTraits

TBR=sky@chromium.org

Bug: 806965,799482
Change-Id: I4f725df6a90bc1d5ec75988bff281bf87832714b
Reviewed-on: https://chromium-review.googlesource.com/900060
Commit-Queue: Ken Rockot <rockot@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#534282}

CrOS-Libchrome-Original-Commit: 8b447d73d8b40966c3c462a126536528a0ba88e5
9 files changed
tree: 0c62487990dbe5a62b30107ccd714af94f111665
  1. base/
  2. build/
  3. components/
  4. dbus/
  5. device/
  6. ipc/
  7. mojo/
  8. testing/
  9. third_party/
  10. ui/