PDF: Make viewing PDFs when inside a webview work again.
PDF: Make viewing PDFs when inside a webview work again.

This was broken in
https://crrev.com/33f9fc827ddb8db53e357bcd50cf20fb4c6a0711.

Review URL: https://codereview.chromium.org/1189293002

Cr-Commit-Position: refs/heads/master@{#335467}
(cherry picked from commit 00a972c0a0797474b5424c5b773fd04442df2087)

BUG=500027
TBR=raymes@chromium.org

Review URL: https://codereview.chromium.org/1209853002.

Cr-Commit-Position: d34a0005849006230ae7ffb1a9693419810a06bc@{#399}
Cr-Branched-From: 40cda19e609fd36fbf5fe489055423e611631abc@{#330231}

Fireblend/chromium-crosswalk,Fireblend/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,Fireblend/chromium-crosswalk,Fireblend/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,Fireblend/chromium-crosswalk,Fireblend/chromium-crosswalk,Fireblend/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,Fireblend/chromium-crosswalk,Fireblend/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,PeterWangIntel/chromium-crosswalk