Adding MHTML support into Page Load Metrics

Adding MHTML support into Page Load Metrics

Offline Previews metrics will not be reported currently because the
MIME-type sniffing only allows text/html or application/xhtml+xml.
MHTML, entires pages saved as one file are mime-type multipart/related
(https://en.wikipedia.org/wiki/MIME#Multipart_subtypes). Offline
previews are treated as HTTP/HTTPS MHTML pages from the perspective of
the chrome page load metrics harness, and treated as HTML documents in
blink. This should mean that offline pages are the only class of MHTML
pages that will be tracked in the harness.

BUG=693776
Review-Url: https://codereview.chromium.org/2699213002
Cr-Commit-Position: refs/heads/master@{#451906}
(cherry picked from commit 07205c9be7b8fa35aa6079b6027f6261761b62c3)

Review-Url: https://codereview.chromium.org/2708213005 .
Cr-Commit-Position: refs/branch-heads/2987@{#642}
Cr-Branched-From: ad51088c0e8776e8dcd963dbe752c4035ba6dab6-refs/heads/master@{#444943}
Committed: https://chromium.googlesource.com/chromium/src/+/df8c967bc255fe10a4d9a4c34b5094afc0868958

[RyanSturm, 2017-02-22 16:42:15]

Description was changed from

==========
Adding MHTML support into Page Load Metrics

Offline Previews metrics will not be reported currently because the
MIME-type sniffing only allows text/html or application/xhtml+xml.
MHTML, entires pages saved as one file are mime-type multipart/related
(https://en.wikipedia.org/wiki/MIME#Multipart_subtypes). Offline
previews are treated as HTTP/HTTPS MHTML pages from the perspective of
the chrome page load metrics harness, and treated as HTML documents in
blink. This should mean that offline pages are the only class of MHTML
pages that will be tracked in the harness.

BUG=693776

Review-Url: https://codereview.chromium.org/2699213002
Cr-Commit-Position: refs/heads/master@{#451906}
(cherry picked from commit 07205c9be7b8fa35aa6079b6027f6261761b62c3)
==========

to

==========
Adding MHTML support into Page Load Metrics

Offline Previews metrics will not be reported currently because the
MIME-type sniffing only allows text/html or application/xhtml+xml.
MHTML, entires pages saved as one file are mime-type multipart/related
(https://en.wikipedia.org/wiki/MIME#Multipart_subtypes). Offline
previews are treated as HTTP/HTTPS MHTML pages from the perspective of
the chrome page load metrics harness, and treated as HTML documents in
blink. This should mean that offline pages are the only class of MHTML
pages that will be tracked in the harness.

BUG=693776

Review-Url: https://codereview.chromium.org/2699213002
Cr-Commit-Position: refs/heads/master@{#451906}
(cherry picked from commit 07205c9be7b8fa35aa6079b6027f6261761b62c3)

Review-Url: https://codereview.chromium.org/2708213005 .
Cr-Commit-Position: refs/branch-heads/2987@{#642}
Cr-Branched-From:
ad51088c0e8776e8dcd963dbe752c4035ba6dab6-refs/heads/master@{#444943}
Committed:
https://chromium.googlesource.com/chromium/src/+/df8c967bc255fe10a4d9a4c34b50...
==========

[RyanSturm, 2017-02-22 16:42:17]

Committed patchset #1 (id:1) manually as
df8c967bc255fe10a4d9a4c34b5094afc0868958.