PDF: Set the referrer in DocumentLoader::GetRequest().
PDF: Set the referrer in DocumentLoader::GetRequest().

BUG=479518

Review URL: https://codereview.chromium.org/1115603002

Cr-Commit-Position: refs/heads/master@{#327641}
(cherry picked from commit a9ceb724a56a866f4fca58736cd861d2414e4f6c)

Review URL: https://codereview.chromium.org/1127503003

Cr-Commit-Position: fe94940391158563b8e4cf7888f93321f554af93@{#293}
Cr-Branched-From: 9fdd9ec11ee753dedeffe15e7e822b13445dc287@{#323860}

fujunwei/chromium-crosswalk,fujunwei/chromium-crosswalk,fujunwei/chromium-crosswalk,fujunwei/chromium-crosswalk,fujunwei/chromium-crosswalk,fujunwei/chromium-crosswalk,fujunwei/chromium-crosswalk,fujunwei/chromium-crosswalk,fujunwei/chromium-crosswalk