DevTools: Trim stylesheet URLs in the Styles sidebar to 30 characters

LayoutTests/inspector/styles/dynamic-style-tag-expected.txt

 Tests that different types of inline styles are correctly disambiguated and their sourceURL is correct.
 
 Stylesheet added:
   - isInline: true
   - sourceURL: dynamic-style-tag.html
   - hasSourceURL: false
   - contents: 
 /* comment */.inline-style-added-by-parser {
    color: red;
 }
@@ skipping 42 matching lines @@
    color: grey;
 }
 /*# sourceURL=inlineStyleCreatedByScript.css*/
 Page reloaded.
 [expanded] 
 element.style  { ()
 color: red;
 
 ======== Matched CSS Rules ========
 [expanded] 
-.inline-style-created-by-script-with-source-url  { (inlineStyleCreatedByScript.css:1 -> inlineStyleCreatedByScript.css:1:1)
+.inline-style-created-by-script-with-source-url  { (inlineStyleCrea…ByScript.css:1 -> inlineStyleCreatedByScript.css:1:1)
 /-- overloaded --/ color: grey;
 
 [expanded] 
 .inline-style-created-by-script  { ()
 /-- overloaded --/ color: orange;
 
 [expanded] 
-.inline-style-added-by-document-write-with-source-url  { (inlineStyleAddedByDocumentWrite.css:2 -> inlineStyleAddedByDocumentWrite.css:2:1)
+.inline-style-added-by-document-write-with-source-url  { (inlineStyleAdde…entWrite.css:2 -> inlineStyleAddedByDocumentWrite.css:2:1)
 /-- overloaded --/ color: yellow;
 
 [expanded] 
 .inline-style-added-by-parser-in-document-write  { ()
 /-- overloaded --/ color: blue;
 
 [expanded] 
 .inline-style-added-by-parser-with-source-url  { ()
 /-- overloaded --/ color: green;
 
 [expanded] 
 .inline-style-added-by-parser  { (dynamic-style-tag.html:6 -> dynamic-style-tag.html:6:14)
 /-- overloaded --/ color: red;
 
 [expanded] 
 div  { (user agent stylesheet)
 display: block;