[Offline Pages] Add UMA to record final offline request status and loading failed error code.

[Offline Pages] Add UMA to record final offline request status and loading failed error code.

BUG=704999
Review-Url: https://codereview.chromium.org/2751253004
Cr-Commit-Position: refs/heads/master@{#458001}
(cherry picked from commit 642d1848697b731de396d6df1577443e33e17ad0)

Review-Url: https://codereview.chromium.org/2779783002 .
Cr-Commit-Position: refs/branch-heads/3029@{#433}
Cr-Branched-From: 939b32ee5ba05c396eef3fd992822fcca9a2e262-refs/heads/master@{#454471}
Committed: https://chromium.googlesource.com/chromium/src/+/8b28e3a4dc7090a2ad9cbcf66fc427d941b8c1dd

[Pete Williamson, 2017-03-27 18:36:38]

Description was changed from

==========
[Offline Pages] Add UMA to record final offline request status and loading
failed error code.

BUG=704999

Review-Url: https://codereview.chromium.org/2751253004
Cr-Commit-Position: refs/heads/master@{#458001}
(cherry picked from commit 642d1848697b731de396d6df1577443e33e17ad0)
==========

to

==========
[Offline Pages] Add UMA to record final offline request status and loading
failed error code.

BUG=704999

Review-Url: https://codereview.chromium.org/2751253004
Cr-Commit-Position: refs/heads/master@{#458001}
(cherry picked from commit 642d1848697b731de396d6df1577443e33e17ad0)

Review-Url: https://codereview.chromium.org/2779783002 .
Cr-Commit-Position: refs/branch-heads/3029@{#433}
Cr-Branched-From:
939b32ee5ba05c396eef3fd992822fcca9a2e262-refs/heads/master@{#454471}
Committed:
https://chromium.googlesource.com/chromium/src/+/8b28e3a4dc7090a2ad9cbcf66fc4...
==========

[Pete Williamson, 2017-03-27 18:36:40]

Committed patchset #1 (id:1) manually as
8b28e3a4dc7090a2ad9cbcf66fc427d941b8c1dd.