DevTools: shard inspector/elements tests for faster execution.

LayoutTests/inspector/elements/styles-3/styles-cancel-editing-expected.txt

 Tests that editing is canceled properly after incremental editing.
 
 Text
 [expanded] 
 element.style  { ()
     color: red;
 
 [expanded] 
 div  { (user agent stylesheet)
     display: block;
 
 After append:
 [expanded] 
 element.style  { ()
     color: red;
 
 [expanded] 
 div  { (user agent stylesheet)
     display: block;