Rename LayoutInvalidationReason namepsace to layout_invalidation_reason

https://google.github.io/styleguide/cppguide.html#Namespace_Names
> Namespace names are all lower-case.

This CL has no behavior changes.

Bug: 889726
Change-Id: Ie237b994b8e871b1d3b6a999341847ad975a25a9
Reviewed-on: https://chromium-review.googlesource.com/c/1343581
Reviewed-by: Kent Tamura <tkent@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: DongJun Kim <djmix.kim@samsung.com>
Cr-Commit-Position: refs/heads/master@{#610281}
71 files changed