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/1308323007 .

Cr-Commit-Position: refs/branch-heads/2490@{#78}
Cr-Branched-From: 7790a3535f2a81a03685eca31a32cf69ae0c114f-refs/heads/master@{#344925}
3 files changed