Fix tests that are disabled/flaky/slow in >1 browser

[zcorpan]

Context: Fix tests that are disabled in WebKit, Chromium, Gecko, Edge

Find tests that are disabled or flaky or slow in more than one browser, investigate why and fix.

Report for Mozilla/Chromium/WebKit/Edge is available at http://bocoup.github.io/wpt-disabled-tests-report/

2 browsers (9 tests) 3 browsers (6 tests)

• [x] /WebCryptoAPI/generateKey/test_successes_RSA-OAEP.https.html #10794
• [ ] /media-source/mediasource-activesourcebuffers.html #10919
• [x] /media-source/mediasource-duration.html #10920
• [ ] /resource-timing/resource-timing.html #10798
• [x] /workers/semantics/structured-clone/dedicated.html #10799
• [x] /workers/semantics/structured-clone/shared.html #10799

2 browsers (60 tests)

• [ ] /IndexedDB/idbdatabase-createObjectStore-exception-order.htm #10792
• [ ] /IndexedDB/keypath-exceptions.htm #10793
• [ ] /html/dom/dynamic-markup-insertion/opening-the-input-stream/010.html #10795
• [ ] /html/dom/reflection-forms.html #10796
• [ ] /html/semantics/scripting-1/the-script-element/module/instantiation-error-8.html #10797
• [ ] ...

[zcorpan]

I fixed a bug in the report, now the numbers are different. 4 tests common in 3 browsers, 52 tests common in 2 browsers.

Edit: after adding Edge, 6 tests common in 3 browsers, 60 tests common in 2 browsers.