I'm not able to repro this though I did see this a long time ago. If you see it again, can you keep the page open so I can look at the DOM on your machine?

Will do!

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/39dfd062d8014833796a544e4b778ed811b98325

commit 39dfd062d8014833796a544e4b778ed811b98325
Author: btolsch <btolsch@chromium.org>
Date: Thu May 26 18:48:50 2016

[Media Router WebUI] Delay putSearchAtBottom_() until after imports

This change ensures that a call to putSearchAtBottom_() is made after
all the html imports have been completed. This should ensure that the
reference to search.offsetHeight is not zero when it sets margins and
padding.

BUG= 614209 ,  609350 
R=apacible@chromium.org
CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2008393002
Cr-Commit-Position: refs/heads/master@{#396244}

[modify] https://crrev.com/39dfd062d8014833796a544e4b778ed811b98325/chrome/browser/resources/media_router/elements/media_router_container/media_router_container.js

Your change meets the bar and is auto-approved for M52 (branch: 2743)

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/b900e1e230e10a966694c3d4ccff40239d7c9301

commit b900e1e230e10a966694c3d4ccff40239d7c9301
Author: btolsch <btolsch@chromium.org>
Date: Wed Jun 01 23:04:11 2016

[Media Router WebUI] Delay putSearchAtBottom_() until after imports

This change ensures that a call to putSearchAtBottom_() is made after
all the html imports have been completed. This should ensure that the
reference to search.offsetHeight is not zero when it sets margins and
padding.

BUG= 614209 ,  609350 
R=apacible@chromium.org
NOTRY=true
NOPRESUBMIT=true

Review-Url: https://codereview.chromium.org/2008393002
Cr-Commit-Position: refs/heads/master@{#396244}
(cherry picked from commit 39dfd062d8014833796a544e4b778ed811b98325)

Review-Url: https://codereview.chromium.org/2028373002
Cr-Commit-Position: refs/branch-heads/2743@{#180}
Cr-Branched-From: 2b3ae3b8090361f8af5a611712fc1a5ab2de53cb-refs/heads/master@{#394939}

[modify] https://crrev.com/b900e1e230e10a966694c3d4ccff40239d7c9301/chrome/browser/resources/media_router/elements/media_router_container/media_router_container.js