feat(platform-server): add getComputedStyle implementation

[ardatan]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/angular/angular/blob/master/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[ ] Bugfix
[x] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] angular.io application / infrastructure changes
[ ] Other... Please describe:

What is the current behavior?

Issue Number: N/A

What is the new behavior?

Now getComputedStyle method can be used in platform-server with flex-layout etc.

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[CaerusKaru]

cc @vikerman, just like in #18362, this is needed for angular/flex-layout

[vikerman]

Hi - Sorry. I missed the previous one.

Can you explain a bit more as to what this PR is trying to do?

Also need tests

[CaerusKaru]

@vikerman currently Domino doesn't provide an implementation for getComputedStyle on the server, which means that angular/flex-layout, which relies on this method, has to catch the thrown exception from this method when rendering.

This PR implements the method on the server, albeit so far without tests.

[ardatan]

@CaerusKaru CI still gives error and I couldn’t get the error message.
By the way, I’ve added license header.

[CaerusKaru]

@ardatan The Circle CI issue is a network timeout, probably because it couldn't access the yarn registry. Try resubmitting your commit (and you might want to rebase from master too).

You also need to add unit tests for your method (just to confirm that it works on server-generated elements).

[vikerman]

Thanks. Overall makes sense. Will look into the implementation. Tests would be needed. Put the required ones at https://github.com/angular/angular/blob/master/packages/platform-server/test/integration_spec.ts

Thanks!

[LinboLen]

curiously, what is this ɵ

[CaerusKaru]

It's a private method identifier. It's an Angular convention. You can find it anywhere, every package uses it.

[CaerusKaru]

It looks like CSSStyleDeclaration is already implemented by Domino. Can you patch this PR to simply rely on that method?

If that's not the case (and their impl. is insufficient), it might be worth implementing the patch in Domino itself instead of here.

[AndrewKushnir]

Closing this PR based on #19856 (comment).

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