Fixes document type detection on iOS 9.

Fixes document type detection on iOS 9.

On iOS 9, evaluating '' + document always results in [object
HTMLDocument], even for PDFs. This introduces another way of checking
document type on iOS 9. Unfortunately, it doesn't work on iOS 8, so the
old implementation needs to stay too.

BUG=549604
Review URL: https://codereview.chromium.org/1458703004

Cr-Commit-Position: refs/heads/master@{#361095}
(cherry picked from commit 704def3b29d00bf39aca6553a079152171af4ad9)

Committed: https://chromium.googlesource.com/chromium/src/+/f5f194b3efbdfc92886eebe0b359a25518061fe0

[bzanotti, 2015-12-02 16:40:48]

Description was changed from

==========
Fixes document type detection on iOS 9.

On iOS 9, evaluating '' + document always results in [object
HTMLDocument], even for PDFs. This introduces another way of checking
document type on iOS 9. Unfortunately, it doesn't work on iOS 8, so the
old implementation needs to stay too.

BUG=549604

Review URL: https://codereview.chromium.org/1458703004

Cr-Commit-Position: refs/heads/master@{#361095}
(cherry picked from commit 704def3b29d00bf39aca6553a079152171af4ad9)
==========

to

==========
Fixes document type detection on iOS 9.

On iOS 9, evaluating '' + document always results in [object
HTMLDocument], even for PDFs. This introduces another way of checking
document type on iOS 9. Unfortunately, it doesn't work on iOS 8, so the
old implementation needs to stay too.

BUG=549604

Review URL: https://codereview.chromium.org/1458703004

Cr-Commit-Position: refs/heads/master@{#361095}
(cherry picked from commit 704def3b29d00bf39aca6553a079152171af4ad9)

Committed:
https://chromium.googlesource.com/chromium/src/+/f5f194b3efbdfc92886eebe0b359...
==========

[bzanotti, 2015-12-02 16:40:49]

Committed patchset #1 (id:1) manually as
f5f194b3efbdfc92886eebe0b359a25518061fe0 (tree was closed).

[bzanotti, 2015-12-02 16:43:34]

A revert of this CL (patchset #1 id:1) has been created in
https://codereview.chromium.org/1491263002/ by bzanotti@chromium.org.

The reason for reverting is: No approval for this cherry-pick. Reverting..