fix(animations): getAnimationStyle causes exceptions in older browsers

[Serginho]

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
• 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: #24094

What is the new behavior?

Animation doesn't break in old browsers now

Does this PR introduce a breaking change?

• Yes
• No

Other information

[matsko]

@Serginho sorry this took us forever to get back to you on.

Could you add a test to this? You would need to export the function you modified and import it into https://github.com/angular/angular/blob/master/packages/animations/browser/test/render/css_keyframes/element_animation_style_handler_spec.ts

Then test by mocking out the a fake element a style property.

[Serginho]

@matsko I didn't do any additional test because getAnimationStyle is already tested, for example here:

angular/packages/animations/browser/test/render/css_keyframes/element_animation_style_handler_spec.ts

Lines 66 to 68 in 5bc39f8

	assertStyle(element, 'animation-name', 'fooAnimation');
	handler.apply();
	assertStyle(element, 'animation-name', 'fooAnimation, barAnimation');

So I assume you want a testcase for this bug, and this is what I did in the updated commit.
The fix is squashed, formatted, and rebased to master.

Let me know if you need something else.

[petebacondarwin]

LGTM - please can you add some more information to the commit message body?

[petebacondarwin]

@Serginho - would you mind rebasing this PR on top of master. Then I will try to chase reviewers to get it merged.

[Serginho]

@petebacondarwin Sure.

Rebased and ready to merge.

[petebacondarwin]

Thanks for rebasing @Serginho. Just one minor correction in the test.

[petebacondarwin]

Great! Thanks.

[AndrewKushnir]

Presubmit.

[AndrewKushnir]

@Serginho this PR is now merged, thanks for contributing to Angular!

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