Screenshot : https://pantheon.corp.google.com/m/cloudstorage/b/chromiumos-test-logs/o/bugfiles/cr/630466/Screenshot%202016-07-21%20at%204.09.00%20PM.png

I am able to repro this issue in ChromeOS LINK device. It only repro when load the audio file in browser directly.
liberato@, can you take a look?

sure!

This issue is also observed in Chrome device Chell with M52 52.0.2743.113 / 8350.66.0 stable

i've got a local repro of this.  it looks like the mute button is being removed for lack of space, but the media control panel is the correct width (300px).

still looking.

it is definitely a width issue.  overriding the width to be 320px causes the mute button to appear.

i'm not sure why it requires 320px to show the controls.  they should fit in 300px just fine -- worst case is that it reserves 48px for each, which is still 6 controls.  there are only 4 shown.

could someone with a repro verify the zoom setting that chrome is using?  is it 100%?  if not, what is it?  if so, can you lower it to 90% then back to 100, and see if the mute button is still missing?

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/5d215e472cf4e2e831aa80b9eed4eb82beffdece

commit 5d215e472cf4e2e831aa80b9eed4eb82beffdece
Author: liberato <liberato@chromium.org>
Date: Tue Aug 09 12:44:18 2016

Adjust MediaControls for effective zoom when dropping controls.

When computing how many controls fit in the media control panel, the
effective zoom was ignored.  This caused the control width to appear
to change as they zoomed, even though the available space in the bar
also changed proportionally.  The effect was that zooming would
change which controls were visible in the panel.

This CL adjusts for the ComputedStyle's effective zoom.

BUG= 630466 
TEST=media-controls-fit-properly-while-zoomed.html

Review-Url: https://codereview.chromium.org/2219673004
Cr-Commit-Position: refs/heads/master@{#410644}

[modify] https://crrev.com/5d215e472cf4e2e831aa80b9eed4eb82beffdece/third_party/WebKit/LayoutTests/TestExpectations
[add] https://crrev.com/5d215e472cf4e2e831aa80b9eed4eb82beffdece/third_party/WebKit/LayoutTests/media/media-controls-fit-properly-while-zoomed.html
[modify] https://crrev.com/5d215e472cf4e2e831aa80b9eed4eb82beffdece/third_party/WebKit/Source/core/html/shadow/MediaControls.cpp

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/6bec99f62cdba98f22dbcba5835b3293821ff8e7

commit 6bec99f62cdba98f22dbcba5835b3293821ff8e7
Author: Rebaseline Bot <blink-rebaseline-bot@chromium.org>
Date: Tue Aug 09 14:44:27 2016

Auto-rebaseline for r410644

https://chromium.googlesource.com/chromium/src/+/5d215e472

BUG= 630466 
TBR=liberato@chromium.org

Review URL: https://codereview.chromium.org/2229813002 .

Cr-Commit-Position: refs/heads/master@{#410673}

[modify] https://crrev.com/6bec99f62cdba98f22dbcba5835b3293821ff8e7/third_party/WebKit/LayoutTests/TestExpectations
[modify] https://crrev.com/6bec99f62cdba98f22dbcba5835b3293821ff8e7/third_party/WebKit/LayoutTests/platform/linux/media/video-zoom-controls-expected.png
[modify] https://crrev.com/6bec99f62cdba98f22dbcba5835b3293821ff8e7/third_party/WebKit/LayoutTests/platform/linux/media/video-zoom-controls-expected.txt
[add] https://crrev.com/6bec99f62cdba98f22dbcba5835b3293821ff8e7/third_party/WebKit/LayoutTests/platform/mac-mac10.10/media/video-zoom-controls-expected.png
[add] https://crrev.com/6bec99f62cdba98f22dbcba5835b3293821ff8e7/third_party/WebKit/LayoutTests/platform/mac-mac10.10/media/video-zoom-controls-expected.txt
[add] https://crrev.com/6bec99f62cdba98f22dbcba5835b3293821ff8e7/third_party/WebKit/LayoutTests/platform/mac-mac10.9/media/video-zoom-controls-expected.png
[add] https://crrev.com/6bec99f62cdba98f22dbcba5835b3293821ff8e7/third_party/WebKit/LayoutTests/platform/mac-mac10.9/media/video-zoom-controls-expected.txt
[add] https://crrev.com/6bec99f62cdba98f22dbcba5835b3293821ff8e7/third_party/WebKit/LayoutTests/platform/mac-retina/media/video-zoom-controls-expected.png
[add] https://crrev.com/6bec99f62cdba98f22dbcba5835b3293821ff8e7/third_party/WebKit/LayoutTests/platform/mac-retina/media/video-zoom-controls-expected.txt
[modify] https://crrev.com/6bec99f62cdba98f22dbcba5835b3293821ff8e7/third_party/WebKit/LayoutTests/platform/mac/media/video-zoom-controls-expected.png
[modify] https://crrev.com/6bec99f62cdba98f22dbcba5835b3293821ff8e7/third_party/WebKit/LayoutTests/platform/mac/media/video-zoom-controls-expected.txt
[modify] https://crrev.com/6bec99f62cdba98f22dbcba5835b3293821ff8e7/third_party/WebKit/LayoutTests/platform/win/media/video-zoom-controls-expected.png
[modify] https://crrev.com/6bec99f62cdba98f22dbcba5835b3293821ff8e7/third_party/WebKit/LayoutTests/platform/win/media/video-zoom-controls-expected.txt
[add] https://crrev.com/6bec99f62cdba98f22dbcba5835b3293821ff8e7/third_party/WebKit/LayoutTests/platform/win7/media/video-zoom-controls-expected.png
[add] https://crrev.com/6bec99f62cdba98f22dbcba5835b3293821ff8e7/third_party/WebKit/LayoutTests/platform/win7/media/video-zoom-controls-expected.txt

Your change meets the bar and is auto-approved for M53 (branch: 2785)

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/cc59f1b9386a873ed972028234621436caa271af

commit cc59f1b9386a873ed972028234621436caa271af
Author: liberato <liberato@chromium.org>
Date: Wed Aug 10 17:35:18 2016

[M53] Adjust MediaControls for effective zoom when dropping controls.

This is a merge of https://codereview.chromium.org/2219673004 .

When computing how many controls fit in the media control panel, the
effective zoom was ignored.  This caused the control width to appear
to change as they zoomed, even though the available space in the bar
also changed proportionally.  The effect was that zooming would
change which controls were visible in the panel.

This CL adjusts for the ComputedStyle's effective zoom.

BUG= 630466 
TEST=media-controls-fit-properly-while-zoomed.html
TBR=mlamouri@chromium.org
NOPRESUBMIT=true
NOTRY=true

Review-Url: https://codereview.chromium.org/2237553002
Cr-Commit-Position: refs/branch-heads/2785@{#549}
Cr-Branched-From: 68623971be0cfc492a2cb0427d7f478e7b214c24-refs/heads/master@{#403382}

[modify] https://crrev.com/cc59f1b9386a873ed972028234621436caa271af/third_party/WebKit/LayoutTests/TestExpectations
[add] https://crrev.com/cc59f1b9386a873ed972028234621436caa271af/third_party/WebKit/LayoutTests/media/media-controls-fit-properly-while-zoomed.html
[modify] https://crrev.com/cc59f1b9386a873ed972028234621436caa271af/third_party/WebKit/Source/core/html/shadow/MediaControls.cpp

Verified on 8872.28.0, 55.0.2883.30