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

[email protected]

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