GitLab

Add
- decl in .h file and impl in .cc
- hint about needing CONTENT_EXPORT

Change-Id: I463315e961c2c80e713f1aee8e1da72b6d86a5ef
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2237436
Commit-Queue: Fergal Daly <fergal@chromium.org>
Reviewed-by: Nasko Oskov <nasko@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Auto-Submit: Fergal Daly <fergal@chromium.org>
Cr-Commit-Position: refs/heads/master@{#779260}