GitLab

Add message handling in the PDF plugin for displaying/hiding PDF
annotations and hook it up to PDFiumEngine, which already has support
for this feature.

Bug: 642982
Change-Id: I18f4dfb9aed4639936d9392a260289224f5dc1f9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2242793
Commit-Queue: Lei Zhang <thestig@chromium.org>
Reviewed-by: Daniel Hosseinian <dhoss@chromium.org>
Cr-Commit-Position: refs/heads/master@{#778997}