[webapi][XWALK-2508] Fix bug for CSSStyleAttribute

- Fix case bug for CSSStyleAttribute

Impacted tests(approved): new 0, update 1, delete 0
Unit test platform: [Android]
Unit test result summary: pass 1, fail 0, block 0
Merge pull request #881 from yunxliu/yunxliu/misc/CSSStyleAttribute

[webapi][XWALK-2508] Fix bug for CSSStyleAttribute