[webapi] Add 7 cases for audio from w3c

- 2 tests come from https://github.com/w3c/web-platform-tests/tree/master/html/semantics/embedded-content/the-audio-element (commit 5caa5d10e06703a0175bfea7ada3afa392debacb)
- 5 tests come from https://github.com/w3c/web-platform-tests/tree/master/html/semantics/embedded-content/media-elements (commit 5caa5d10e06703a0175bfea7ada3afa392debacb)

Impacted tests(approved): new 7, update 0, delete 0
Unit test platform: [android] crosswalk-10.38.222
Unit test result summary: pass 7, fail 0, block 0