Minimize the number of range requests made by PDFium

Previously, Chrome would make a series of range requests for linearized PDFs,
starting at 32 KB and slowly increasing. On high latency connections, this is
considerably slower than using a single request. Now Chrome will make range
requests as large as possible and cancel them if the renderer needs some data in
a different place in the document. This significantly reduces the number of
range requests performed by Chrome.

BUG=460201,78264

Review URL: https://codereview.chromium.org/1506023002

Cr-Commit-Position: refs/heads/master@{#364235}
4 files changed