Prevent leaking PDF data cross-origin

BUG=520422

Review URL: https://codereview.chromium.org/1311973002

Cr-Commit-Position: refs/heads/master@{#345267}
(cherry picked from commit fff450abc4e2fb330ba700547a8e6a7b0fb90a6e)

Review URL: https://codereview.chromium.org/1316803003 .

Cr-Commit-Position: refs/branch-heads/2454@{#446}
Cr-Branched-From: 12bfc3360892ec53cd00fc239a47e5298beb063b-refs/heads/master@{#338390}
3 files changed