Remove fixed header at chrome://inspect
Remove fixed header at chrome://inspect

The fixed header gets in the way when the user zooms in and attempts to
scroll the page. To fix this issue, the header is no longer at a
viewport-fixed position, but at a static position within the main
content. The location specified by the page header is already displayed
in the left navigation bar, so this change does not hurt usability.

BUG=492124

Review URL: https://codereview.chromium.org/1187813004

Cr-Commit-Position: refs/heads/master@{#334722}
(cherry picked from commit 0d96227ee3378a3b0676f7923560c69f0a8209c7)

Review URL: https://codereview.chromium.org/1185783008

Cr-Commit-Position: d34a0005849006230ae7ffb1a9693419810a06bc@{#341}
Cr-Branched-From: 40cda19e609fd36fbf5fe489055423e611631abc@{#330231}

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