Switch PDFium from the XFA branch to master.
Switch PDFium from the XFA branch to master.

The XFA branch has been merged into master.

TBR=tsepez@chromium.org
BUG=583804

Review URL: https://codereview.chromium.org/1673573002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#373859}

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