[webapi][XWALK-2955] Update two reference files

Because reference file using png image(support/1x1-green.png) as background does not match test case background color of css style.
Impacted tests(approved):new 0,update 17,delete 0
Unit test platform:[TizenIVI]
Unit test result summary:pass 17,fail 0,block 0
Merge pull request #1318 from chenxix/webapi/reapir-background

[webapi][XWALK-2955] Update two reference files