GitLab

1. Add method PDFiumEngine::GetAttachmentData(). Giving an attachment
   index number, the method returns the content of that attachment in
   a buffer.

2. Add unit tests for GetAttachmentData() in an existing
   PDFiumEngineTest, and rename the test "GetDocumentAttachments" since
   it not only checks the meta data of attachments, but also checks
   the contents of attachments now.

Bug: 177188
Change-Id: I418173abd77033d8edba33de61bac0d30ae51120
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2229765Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Hui Yingst <nigi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#798781}