Populate Images in PDFiumPage

This CL introduces a new method PDFiumPage::CalculateImage() which is
responsible for populating images vector in PDFiumPage.

Added a unit test TestCalculateImages() as well as pdf test file
containing three images to verify the image data.

Bug: 981448
Change-Id: Ifbc8426cb47a3a7a76b2bca309c7a68e1792b3fe
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1738690
Reviewed-by: Lei Zhang <thestig@chromium.org>
Reviewed-by: Kevin Babbitt <kbabbitt@microsoft.com>
Commit-Queue: Pratish Kumar <prkum@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#689109}
5 files changed