dom: Remove mutation_observer.h dependency from node.h.

node.h is used in 4,700+ compilation units, and this CL reduces its
estimated expanded size from 3.47MB to 2.58MB.

Node depended on enum blink::MutationObserver::MutationType. This CL
makes it to blink::MutationType, and moves it out from
mutation_observer.h.

Also, NodeMutationObserverData in node_rare_data.h depended on
mutation_observer_registration.h. This CL moves member functions of
NodeMutationObserverData from node_rare_data.h to node_rare_data.cc
to remove #include mutation_observer_registration.h.

Bug: 242216
Change-Id: I7a603bda1442dedc45674daab1b5d8f5b369f123
Reviewed-on: https://chromium-review.googlesource.com/1102291
Reviewed-by: Hayato Ito <hayato@chromium.org>
Commit-Queue: Kent Tamura <tkent@chromium.org>
Cr-Commit-Position: refs/heads/master@{#568311}
15 files changed