[Bug] Browser menus can be too narrow

[Mugurell]

Seen while testing mozilla-mobile/fenix#17772
With newCoreMenuItems the menu may be too narrow.

Currently seems to only reproduce only when the toolbar is set on top:

MenuIsTooNarrow.mp4

┆Issue is synchronized with this Jira Task

[Mugurell]

Looked into this a bit, seems like something that can easily be fixed in AC.

[Mugurell]

This is a very interesting issue of the DynamicWidthRecyclerView that allows the menu to have a dynamic width (with some safe bounds) happening when there are many items to be displayed.

The RecyclerView is a bit too dynamic, in that it will always have the width of the maximum displayed children. This means that depending on the parent and LayoutParams, with enough items to scroll through it could potentially yo-yo in width depending in what's displayed at that exact moment.

I think this is a bit unexpected and what we'd want is to have it have the width of the largest item.

Saw that in the first onMeasure the width will be reported correctly, because all children are accounted, but then in the first layout phase detachAndScrapAttachedViews will be used to limit how many items will actually be laid out depending on if they fit the screen. And this is done by actually removing the child views so if we try to measure the list again, there are fewer children to measure and we might get different dimensions.

To accommodate our needs seems like we should just cache the first reported width and only use that afterwards.

[abodea]

Verified as fixed on the latest Nightly and Debug builds with Google Pixel 4 XL (11) for more details please check the following:

Device	Build	Reproducible?
Google Pixel 4 XL 11	Nightly 4/7/21	No
Google Pixel 4 XL 11	Nightly 4/6/21	No
Google Pixel 4 XL 11	Debug 4/7/21 (latest Master)	No
Google Pixel 4 XL 11	Debug 3/30/21	Yes

Note that the latest mentioned try on the table is with a version of Master before the merges.
Others

Debug 3/30/21