DevTools: shard inspector/elements tests for faster execution.

LayoutTests/inspector/elements/styles-1/add-new-rule-with-style-after-body-expected.txt

 Tests that adding a new rule works when there is a STYLE element after BODY. TIMEOUT SHOULD NOT OCCUR! Bug 111299
 
 Text
 After adding new rule:
 [expanded] 
 element.style  { ()
     font-size: 12px;
 
 [expanded] [no-affect] 
 inspected  { (inspector-stylesheet:1 -> inspector-stylesheet:1:1)
     color: maroon;
     : ;
 
 [expanded] 
 div  { (user agent stylesheet)
     display: block;