I did not look at all the builds but it seems like testBlockNetworkLoadsWithAudio started failing constantly after build 4046. 

https://build.chromium.org/p/chromium.android/builders/Lollipop%20Low-end%20Tester/builds/4047

Looking at the flakiness dashboard, something was introduced in sep 21 timeframe that caused the test to timeout only on low end devices.

https://test-results.appspot.com/dashboards/flakiness_dashboard.html#testType=android_webview_test_apk&showAllRuns=true&tests=org.chromium.android_webview.test.AwSettingsTest%23testBlockNetworkLoadsWithAudio

From #2, there are many patch related to audio, assigned to media owner for investigation.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/a22b73c3566b9ff5b7743b4ddddabf65c20262df

commit a22b73c3566b9ff5b7743b4ddddabf65c20262df
Author: tobiasjs <tobiasjs@chromium.org>
Date: Tue Oct 04 15:22:37 2016

Stop testBlockNetworkLoadsWithAudio failing on low-end devices.

This test was broken by https://codereview.chromium.org/2344353003
which disables autoplay on low-end devices. Instead of relying on
that, use a button click to start playback.

BUG= 652389 

Review-Url: https://codereview.chromium.org/2388903003
Cr-Commit-Position: refs/heads/master@{#422804}

[modify] https://crrev.com/a22b73c3566b9ff5b7743b4ddddabf65c20262df/android_webview/javatests/src/org/chromium/android_webview/test/AwSettingsTest.java

this is probably the reason for similar breaks in same tester.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/6e5b06e0201d483a1596aedf438fb931fbbe7b42

commit 6e5b06e0201d483a1596aedf438fb931fbbe7b42
Author: avayvod <avayvod@chromium.org>
Date: Fri Oct 07 01:33:42 2016

[Cast, Tests] Handle low end and JB devices that don't preload videos

BUG= 652872 , 652389 
TEST=run_chrome_public_test_apk --verbose --gtest_filter=org.chromium.chrome.browser.media.remote.* on both low end and not a low end device.

Since https://codereview.chromium.org/2344353003 on low-end and JB devices videos
are not preloaded so we have to trigger that in a button onclick handler.

Review-Url: https://codereview.chromium.org/2400543002
Cr-Commit-Position: refs/heads/master@{#423775}

[modify] https://crrev.com/6e5b06e0201d483a1596aedf438fb931fbbe7b42/chrome/android/javatests/src/org/chromium/chrome/browser/media/remote/CastSwitchVideoTest.java
[modify] https://crrev.com/6e5b06e0201d483a1596aedf438fb931fbbe7b42/chrome/android/javatests/src/org/chromium/chrome/browser/media/remote/CastTestBase.java
[modify] https://crrev.com/6e5b06e0201d483a1596aedf438fb931fbbe7b42/chrome/test/data/android/media/simple_video.html
[modify] https://crrev.com/6e5b06e0201d483a1596aedf438fb931fbbe7b42/chrome/test/data/android/media/simple_video2.html
[modify] https://crrev.com/6e5b06e0201d483a1596aedf438fb931fbbe7b42/chrome/test/data/android/media/two_videos.html

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/680764f10bc0dc6f8aa7bfaef566b685983599cd

commit 680764f10bc0dc6f8aa7bfaef566b685983599cd
Author: rockot <rockot@chromium.org>
Date: Fri Oct 07 05:22:30 2016

Revert of [Cast, Tests] Handle low end and JB devices that don't preload videos (patchset #1 id:1 of https://codereview.chromium.org/2400543002/ )

Reason for revert:
Speculative revert because cast tests started flaking very heavily at this revision and it's effectively blocking things in the CQ.

See https://build.chromium.org/p/tryserver.chromium.android/builders/linux_android_rel_ng?numbuilds=200 for example failures

Original issue's description:
> [Cast, Tests] Handle low end and JB devices that don't preload videos
>
> BUG= 652872 , 652389 
> TEST=run_chrome_public_test_apk --verbose --gtest_filter=org.chromium.chrome.browser.media.remote.* on both low end and not a low end device.
>
> Since https://codereview.chromium.org/2344353003 on low-end and JB devices videos
> are not preloaded so we have to trigger that in a button onclick handler.
>
> Committed: https://crrev.com/6e5b06e0201d483a1596aedf438fb931fbbe7b42
> Cr-Commit-Position: refs/heads/master@{#423775}

TBR=mlamouri@chromium.org,avayvod@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG= 652872 , 652389 

Review-Url: https://codereview.chromium.org/2394273003
Cr-Commit-Position: refs/heads/master@{#423799}

[modify] https://crrev.com/680764f10bc0dc6f8aa7bfaef566b685983599cd/chrome/android/javatests/src/org/chromium/chrome/browser/media/remote/CastSwitchVideoTest.java
[modify] https://crrev.com/680764f10bc0dc6f8aa7bfaef566b685983599cd/chrome/android/javatests/src/org/chromium/chrome/browser/media/remote/CastTestBase.java
[modify] https://crrev.com/680764f10bc0dc6f8aa7bfaef566b685983599cd/chrome/test/data/android/media/simple_video.html
[modify] https://crrev.com/680764f10bc0dc6f8aa7bfaef566b685983599cd/chrome/test/data/android/media/simple_video2.html
[modify] https://crrev.com/680764f10bc0dc6f8aa7bfaef566b685983599cd/chrome/test/data/android/media/two_videos.html