first go at readonly

[christophe-g]

Adding a readonly behavior for paper-dropdown-menu

• paper-menu is set to disabled mode
• the menu closes when setting to readonly

[valdrinkoshi]

I believe we can get rid of this observer, as it can be expensive (this is triggered for all the dropdown menus) and it actually solves a very edge case scenario where someone updates this property while the dropdown is opened.
WDYT?

[christophe-g]

Thanks for the comment.
Agreed, this is not going to happen very often (readonly property changing while the dropdown is opened), but it should still be the correct behavior, I guess.
What is the actual weight of adding an observer ?

[valdrinkoshi]

For the actual weight, _readonlyChanged callback is called the first time when readonly is set to its default value, and each time it changes value, which means when is set to true, we have _readonlyChanged called twice.
If you remove the default value for the readonly property, _readonlyChanged will be called only once, when we it is set the first time.

[christophe-g]

Sounds like a good idea !
98b0a21

[valdrinkoshi]

Hi @christophe-g, the implementation LGTM (left a comment).
Tests are failing because you need to sync your branch with master.
Could you also add some unit tests so we avoid future regressions?

[valdrinkoshi]

Thanks for the contribution @christophe-g! can you add some unit tests to avoid any future regression?