Add externalfile: to PDF extension's object-src.

Add externalfile: to PDF extension's object-src.

externalfile:// scheme is used in Chrome OS to open external files (e.g. files in Google Drive) in a browser tab.
After https://codereview.chromium.org/2209113002/, we need to specify it in PDF extension's CSP permissions.

BUG=645285
TBR=raymes@chromium.org
TEST=manually tested the repro steps in the bug description.
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2370223002
Cr-Commit-Position: refs/heads/master@{#421447}
(cherry picked from commit bbf2420306f6d0a3c85d10a4115ab254b3912162)

Committed: https://chromium.googlesource.com/chromium/src/+/b4f6f52b011f0f6a7e30b805934a15e04a644ab8

[fukino, 2016-09-28 15:35:34]

Description was changed from

==========
Add externalfile: to PDF extension's object-src.

externalfile:// scheme is used in Chrome OS to open external files (e.g. files
in Google Drive) in a browser tab.
After https://codereview.chromium.org/2209113002/, we need to specify it in PDF
extension's CSP permissions.

BUG=645285
TBR=raymes@chromium.org
TEST=manually tested the repro steps in the bug description.
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2370223002
Cr-Commit-Position: refs/heads/master@{#421447}
(cherry picked from commit bbf2420306f6d0a3c85d10a4115ab254b3912162)
==========

to

==========
Add externalfile: to PDF extension's object-src.

externalfile:// scheme is used in Chrome OS to open external files (e.g. files
in Google Drive) in a browser tab.
After https://codereview.chromium.org/2209113002/, we need to specify it in PDF
extension's CSP permissions.

BUG=645285
TBR=raymes@chromium.org
TEST=manually tested the repro steps in the bug description.
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2370223002
Cr-Commit-Position: refs/heads/master@{#421447}
(cherry picked from commit bbf2420306f6d0a3c85d10a4115ab254b3912162)

Committed:
https://chromium.googlesource.com/chromium/src/+/b4f6f52b011f0f6a7e30b805934a...
==========

[fukino, 2016-09-28 15:35:36]

Committed patchset #1 (id:1) manually as
b4f6f52b011f0f6a7e30b805934a15e04a644ab8.