[XWALK-1106] Add use case for SpeechSynthesis

- For SpeechSynthesis feature:https://crosswalk-project.org/jira/browse/XWALK-1106
- Fail reason: XWALK-1106 is not ready

Impacted tests(approved):new 1,update 0,delete 0
Unit test platform:[Tizen IVI]
Unit test result summary:pass 0,fail 1,block 0
Merge pull request #915 from yunxiaoxie/yunxiaoxie/speechsynthesis

 [XWALK-1106] Add use case for SpeechSynthesis