GitLab

CalculateBackgroundParts() needs to be migrated to PdfViewPluginBase
since it can be used identically by both PdfViewWebPlugin and
OutOfProcessInstance.

This CL migrates `background_parts_` and `available_area_` to
PdfViewPluginBase and provides accessors and mutators for them, so that
CalculateBackgroundParts() can be migrated as well.

Bug: 1140629
Change-Id: I767468a3716bae40c96c8c36b49d6dd2bb16008d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2625787
Commit-Queue: Hui Yingst <nigi@chromium.org>
Reviewed-by: K. Moon <kmoon@chromium.org>
Reviewed-by: Daniel Hosseinian <dhoss@chromium.org>
Cr-Commit-Position: refs/heads/master@{#843804}