[base] Replace Contains{Key,Value} with Contains in //pdf

This change replaces usages of base::ContainsKey() and base::ContainsValue()
with base::Contains() in //pdf.

Reproduction:
 - sed -i 's/\bbase::ContainsKey\b/base::Contains/g'
 - sed -i 's/\bbase::ContainsValue\b/base::Contains/g'
 - git cl format

This CL was uploaded by git cl split.

TBR=raymes@chromium.org

Bug: 970209
Change-Id: I3ba3eb7f74088d0364d5c16b896d6b81bf08f17e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1648251
Reviewed-by: Jan Wilken Dörrie <jdoerrie@chromium.org>
Commit-Queue: Jan Wilken Dörrie <jdoerrie@chromium.org>
Auto-Submit: Jan Wilken Dörrie <jdoerrie@chromium.org>
Cr-Commit-Position: refs/heads/master@{#667441}