perform a null check in case WebContents doesn't have a ChromeDownloadDelegate

perform a null check in case WebContents doesn't have a ChromeDownloadDelegate

This could happen for Reader mode, as it generates a new webcontents.
Enabling download on Reader mode will cause other issues like
overwrite infobar.
As a result, we should disable download in reader mode.
Will work on removing the download button from media controller in
reader mode.

BUG=650738
Committed: https://crrev.com/ea10fd32a057ff0f991499641243a3781bc92d02
Cr-Commit-Position: refs/heads/master@{#422540}

[qinmin, 2016-10-03 19:36:19]

qinmin@chromium.org changed reviewers:
+ dfalcantara@chromium.org

[qinmin, 2016-10-03 19:36:20]

PTAL

[gone, 2016-10-03 20:35:02]

lgtm

[qinmin, 2016-10-03 20:44:16]

The CQ bit was checked by qinmin@chromium.org

[commit-bot: I haz the power, 2016-10-03 20:45:12]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-10-03 21:35:13]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-10-03 21:36:59]

Description was changed from

==========
perform a null check in case WebContents doesn't have a ChromeDownloadDelegate

This could happen for Reader mode, as it generates a new webcontents.
Enabling download on Reader mode will cause other issues like
overwrite infobar.
As a result, we should disable download in reader mode.
Will work on removing the download button from media controller in
reader mode.

BUG=650738
==========

to

==========
perform a null check in case WebContents doesn't have a ChromeDownloadDelegate

This could happen for Reader mode, as it generates a new webcontents.
Enabling download on Reader mode will cause other issues like
overwrite infobar.
As a result, we should disable download in reader mode.
Will work on removing the download button from media controller in
reader mode.

BUG=650738

Committed: https://crrev.com/ea10fd32a057ff0f991499641243a3781bc92d02
Cr-Commit-Position: refs/heads/master@{#422540}
==========

[commit-bot: I haz the power, 2016-10-03 21:37:00]

Patchset 1 (id:??) landed as
https://crrev.com/ea10fd32a057ff0f991499641243a3781bc92d02
Cr-Commit-Position: refs/heads/master@{#422540}