Found a related bug at  crbug.com/493514 

This has two parts. 

1. Updating the touch interactions. I started an email thread about this so we can make sure we've weighed in all options before we settle on the final touch interactions. 

2. Increase discoverability of the context menu in touch mode.  
Interaction spec: https://gallery.googleplex.com/projects/MCHbtQVoQ2HCZSLl8DO5WVeQ/files/MCHPDvtymHH2zY0CGDl2ok5k

weifangsun@, mcirimele@, should we implement both features in comment #2 for M61?

Regarding the mock in #2, I have following questions.

Files app already uses 3-dot icon. Using the same icon for opening context menu might be confusing.
Maybe we should change the existing icon? (for instance, replace the existing 3-dot icon with gear icon?)

Should we show the new 3-dot icon when a file is selected but not in check-select mode?
If a file is selected without clicking the circle icon, the toolbar will stay blue (not white). Should we show the 3-dot icon to open context menu in this case?

Great questions! 

We decided to re-use the three dot (more) menu for context menu in selected state because it is used in this way in other first party apps (like Drive) on Android. I think it will be okay to have the contents of the menu depend on the state the user is in. 

I call the "selected but not in check-select mode" focus state. The focused state is when the row highlight is light blue and like you said the toolbar is blue. In this case the three dot menu should open the regular overflow menu. 

Can I request image resources for the new context menu button?
Currently we only have ones for a white one.
https://cs.chromium.org/chromium/src/ui/file_manager/file_manager/foreground/images/files/ui/menu_white.png
https://cs.chromium.org/chromium/src/ui/file_manager/file_manager/foreground/images/files/ui/2x/menu_white.png

Since the backgound in the selection mode is white, I think we'd need gray ones like this delete icon.
https://cs.chromium.org/chromium/src/ui/file_manager/file_manager/foreground/images/files/ui/delete.png

+sgabriel@ - Would you be able to provide the requested asset for Files app? This is a 3-dot menu icon like the one in the current menu bar which is grey rather than white for the action bar menu.

Can we also have these assets?
- tooltip/accessibility label text for the button (e.g. "more actions")
- ripple color/transparency of the button (if we want this effect)

Also, should we show "paste" command (=paste items to the current folder) somewhere in the menu, in either of the modes?
Paste is not an action to the selected file, but it currently don't appear in neither of the two modes.

Adding  crbug.com/446606  to this bug from an old touch improvements initiative. Not sure if this bug is still applicable given the current state of Files app (no gear icon) and our current proposed touch enhancements.

526877 & 695699 are not truly blocking, but might be good to review these bugs as we look to improve touch interactions.

Is there anything outstanding on this bug? Looking at canary on Kevin 62.0.3165.0 (9774.0.0) we have "More..." as the tooltip and "paste" in the context menu which is the correct behavior. 

I see a gray three dot icon but can't tell if it's exactly the same color as the other buttons, do you still need an asset for it?

I don't need new assets anymore, unless we see problems with the current ones.
I made the new icons, using the same colors as other icons like the trash icons.
We also applied the ripple effect consistent with other parts of the toolbar.

Thank you so much Yamaguchi-san, that's great work!

What about 'Select all'? That is still conspicuously absent for touch.

 crbug.com/572801  

willg76x@ - Thanks for your feedback! We agree that it would be great to add this action to the Context Menu. We have this feature in our backlog and are working to prioritize including it.