Add checks for android printing

Add checks for android printing

Adds a null check for the WebContent used to set up
renderer initiated print jobs and some warnings to be
able to follow failures in the process.

BUG=528909
Committed: https://crrev.com/e94f112042eba6eff2cf2fb10f853103a50f63b2
Cr-Commit-Position: refs/heads/master@{#349121}

[dgn, 2015-09-14 19:20:03]

dgn@chromium.org changed reviewers:
+ vitalybuka@chromium.org

[dgn, 2015-09-14 19:20:03]

PTAL

[Vitaly Buka (NO REVIEWS), 2015-09-15 00:10:13]

lgtm

[dgn, 2015-09-15 09:44:47]

dgn@chromium.org changed reviewers:
+ bauerb@chromium.org

[dgn, 2015-09-15 09:44:48]

bauerb@chromium.org: Please review changes in
chrome/android/java/src/org/chromium/chrome/browser/printing/TabPrinter.java

[Bernhard Bauer, 2015-09-15 10:56:01]

lgtm

[dgn, 2015-09-16 14:27:51]

Passes now. Thanks for the review!

[dgn, 2015-09-16 14:27:56]

The CQ bit was checked by dgn@chromium.org

[dgn, 2015-09-16 14:27:56]

The patchset sent to the CQ was uploaded after l-g-t-m from
vitalybuka@chromium.org, bauerb@chromium.org
Link to the patchset: https://codereview.chromium.org/1338333002/#ps60001
(title: "Updated test. It still is kind of flaky (2/30, the print dialog comes
up -> timeout), but no crash")

[commit-bot: I haz the power, 2015-09-16 14:28:21]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1338333002/60001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1338333002/60001

[commit-bot: I haz the power, 2015-09-16 14:34:26]

Committed patchset #4 (id:60001)

[commit-bot: I haz the power, 2015-09-16 14:35:04]

Patchset 4 (id:??) landed as
https://crrev.com/e94f112042eba6eff2cf2fb10f853103a50f63b2
Cr-Commit-Position: refs/heads/master@{#349121}

[commit-bot: I haz the power, 2015-09-23 12:55:38]

Patchset 4 (id:??) landed as
https://crrev.com/e94f112042eba6eff2cf2fb10f853103a50f63b2
Cr-Commit-Position: refs/heads/master@{#349121}