Also, I've seen this happen without dev tools open. Toggling the CSS property was just a reliable way to reproduce it.

Tested the issue on Android and no grey box is seen.

Steps followed:
1. Connected Pixel 2XL device to mac laptop
2. Navigated to translate.google.com/m/translate
3. Opened devtools
4. Toggled css property (eg:color) and no grey box is seen.

Chrome version: 
67.0.3396.87 

OS:
Android 9.0

Android device:
Pixel 2 XL

@rmcelrath: 
1.Could you please confirm details of Android device,Android os & Android build you are seeing this issue.
2.If possible please attach a screen-cast of the issue for better understanding and further triaging.
3. Please confirm if you are able to reproduce this issue without dev tools open in Android device with screen-cast for better understanding.

Thanks!

Unfortunately I just noticed this isn't currently reproducible on Android on the public translate.google.com page. I'll update the bug if/when that changes. In the meantime, it is still reliably reproducible for me on my Pixelbook.

Thank you for providing more feedback. Adding the requester to the cc list.

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

There isn't much we can do without a way to reproduce it so please keep us posted. Thanks!

The NextAction date has arrived: 2018-08-13

Feel free to open if a reproduction step becomes available.

This is now reproducible on Android with the public translate.google.com. I'm using a Pixel 2, running Android 9 build number PPR1.180610.009. Chrome version 68.0.3440.91.

Steps to reproduce:
1. Sign in to a Google account in Chrome for android
2. Go to translate.google.com
3. Translate something and hit the star in the top-right corner of the blue translation box
4. Hit the star / "Saved" icon at the bottom of the page
5. Make sure you see your saved translation in this list
6. Hit the search icon at the top of the page
7. There should be a small gray box to the upper left of the "Language pairs" string
8. Close out of search
9. There should be a gray box in the upper left corner of the saved translation

I attached a screen-cast of the bug.

This is also still reproducible on a Pixelbook using the same instructions I originally gave.

Deleted: box.mp4 1.1 MB

	box.mp4 1.1 MB View Download

Will have to wait on someone with the right device on the team to bisect. Small effect, so not high priority. Odd for it to be mobile only.

Doesn't seem to reproduce with DevTools device emulation.

Why adjust the status?

Because we should get a bisect before marking as triaged.

Requesting a test team bisect to identify the cause of this issue (or even if it's a regression).

Still waiting on someone on test to bisect for us, as we do not have the resources to do it.

I can reproduce on M71 beta / Android.

The box is I think related to an overlay scrollbar on an element with id "phrasebook-body".

The shape of it doesn't seem to be the thump for an overlay scrollbar. bokan@ can you take a look at this?

Chao, ptal.

I don't know what it is. But it is not overlay scrollbar. I log layers in LayerTreeHost::DoUpdateLayers. It has 2 overlay scrollbar that attached to visual viewport. Then I remove the scrollbar in visual viewport it can still reproduce.

 Issue 915765  has been merged into this issue.

From the other bug, here's a simplified reproduction: https://terpro.github.io/samples/scrollpixel.html