This patch does the following to clean up the StylePropertyMap.delete
tests for WPT:

- We split happy cases and sad cases into separate files.

- We used to test delete by calling .delete and then checking if .has
  returns false. There are a few problems with this:
  - it's arbitrary why we use .has (and not, say, .get) to check if the
    property was deleted.
  - our tests for .delete depend on .has to be implemented correctly.
  - we are not actually testing that the property was removed from
    element's style (i.e. the style map may not propagate changes to the
    element's style correctly and the tests wouldn't catch that).

  So, to avoid these downsides, we change the tests to call .delete
  and then checking the element's actual style from CSSOM.

- For some reason declared didn't have .delete tests but had an
  expectation file. We add a test for declared .delete, which is
  basically the same as the inline tests but using a rule instead of
  an element.

- We removed the .tentative extension.

Bug: 774887
Change-Id: Ie911b62e493d0ce371b85b1a1a0597fac4ca3f4e
Reviewed-on: https://chromium-review.googlesource.com/872515
Commit-Queue: Darren Shen <[email protected]>
Reviewed-by: nainar <[email protected]>
Cr-Commit-Position: refs/heads/master@{#530113}