OOP PDF: Fix PrintWebViewHelper test issues with OOP PDF enabled.

OOP PDF: Fix PrintWebViewHelper test issues with OOP PDF enabled.

OOP PDF causes that the print-preview page to contain an iframe of the
PDF extension instead of directly including a plugin element. However,
the tests for PrintWebViewHelper use a fake print-preview page that
cannot contain an iframe of the extension because the necessary
infrastructure is not available in the test. This relaxes the
expectations so that in tests where the pdf element isn't an iframe,
that element is used instead.

BUG=303491
Committed: https://crrev.com/81c98ba5f74cbe9e6f1a12a0b96371b65dd4374e
Cr-Commit-Position: refs/heads/master@{#308450}

[Sam McNally, 2014-12-15 06:09:33]

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

[Vitaly Buka (NO REVIEWS), 2014-12-15 22:16:27]

The CQ bit was checked by vitalybuka@chromium.org

[Vitaly Buka (NO REVIEWS), 2014-12-15 22:16:28]

lgtm

[commit-bot: I haz the power, 2014-12-15 22:18:00]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/800343004/1

[commit-bot: I haz the power, 2014-12-15 23:20:08]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-12-15 23:21:02]

Patchset 1 (id:??) landed as
https://crrev.com/81c98ba5f74cbe9e6f1a12a0b96371b65dd4374e
Cr-Commit-Position: refs/heads/master@{#308450}