[webapi][XWALK-1302] Fix bug that failing to get the incorect value of "box-decoration-break" when running webapi/backgrounds on Android OS

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 #336 from minxhuang/hm/webapi/xwalk-1302

[webapi][XWALK-1302] Fix bug that failing to get the incorect value of "box-decoration-break" when running webapi/backgrounds on Android OS