Change pdf compositor unit test to run in a single process

Previously, the unit test for pdf compositor service needed a test
service running in a separate process. Now we change to run the
test service in process so the unit test can be built and run with
other unit tests.

This CL also has a minor fix for not comparing the size of a shared
memory handle with its mapped size because the handle's size
represents the allocated size of the shared memory.

BUG=455764

Change-Id: I0db93e828c99922be54b77814faa29e3f703f493
Reviewed-on: https://chromium-review.googlesource.com/748687
Commit-Queue: Wei Li <weili@chromium.org>
Reviewed-by: Ken Rockot <rockot@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#513841}
4 files changed