Merge to M59: Only skip certain hidden elements at MHTML serialization

Merge to M59: Only skip certain hidden elements at MHTML serialization
1) Elements with hidden attributes
2) Hidden form elements

We orginally tried to act more aggresively by skipping all possible
hidden elements. But this does break certain web sites that uses
nth CSS selectors.

BUG=697970
TEST=tests updated
TBR=svaldez@chromium.org

Review-Url: https://codereview.chromium.org/2819723003
Cr-Commit-Position: refs/heads/master@{#464856}
(cherry picked from commit 2ddf990431d6b7977a94e5da69f18a1a3d220a52)

Review-Url: https://codereview.chromium.org/2826533002 .
Cr-Commit-Position: refs/branch-heads/3071@{#25}
Cr-Branched-From: a106f0abbf69dad349d4aaf4bcc4f5d376dd2377-refs/heads/master@{#464641}
Committed: https://chromium.googlesource.com/chromium/src/+/41faf4c8bb4cab7999d14e0a0195cc132beac4e1

[jianli, 2017-04-17 21:19:38]

Description was changed from

==========
Merge to M59: Only skip certain hidden elements at MHTML serialization
1) Elements with hidden attributes
2) Hidden form elements

We orginally tried to act more aggresively by skipping all possible
hidden elements. But this does break certain web sites that uses
nth CSS selectors.

BUG=697970
TEST=tests updated
TBR=svaldez@chromium.org

Review-Url: https://codereview.chromium.org/2819723003
Cr-Commit-Position: refs/heads/master@{#464856}
(cherry picked from commit 2ddf990431d6b7977a94e5da69f18a1a3d220a52)
==========

to

==========
Merge to M59: Only skip certain hidden elements at MHTML serialization
1) Elements with hidden attributes
2) Hidden form elements

We orginally tried to act more aggresively by skipping all possible
hidden elements. But this does break certain web sites that uses
nth CSS selectors.

BUG=697970
TEST=tests updated
TBR=svaldez@chromium.org

Review-Url: https://codereview.chromium.org/2819723003
Cr-Commit-Position: refs/heads/master@{#464856}
(cherry picked from commit 2ddf990431d6b7977a94e5da69f18a1a3d220a52)

Review-Url: https://codereview.chromium.org/2826533002 .
Cr-Commit-Position: refs/branch-heads/3071@{#25}
Cr-Branched-From:
a106f0abbf69dad349d4aaf4bcc4f5d376dd2377-refs/heads/master@{#464641}
Committed:
https://chromium.googlesource.com/chromium/src/+/41faf4c8bb4cab7999d14e0a0195...
==========

[jianli, 2017-04-17 21:19:40]

Committed patchset #1 (id:1) manually as
41faf4c8bb4cab7999d14e0a0195cc132beac4e1.