DevTools: [CSS] cache lineEndings in InspectorStyleSheet

LayoutTests/http/tests/inspector-enabled/reattach-after-editing-styles-expected.txt

 This test checks that styles edited through inspector are correctly shown upon reattach.
 
 Opening front-end for the first time
 Dump initial styles:
 [expanded] 
 element.style  { ()
 
 [expanded] 
 #testDiv  { (style.css:1 -> style.css:1:1)
 color: red;
 
 [expanded] 
 div  { (user agent stylesheet)
 display: block;
 
 
 Dump styles after editing:
 [expanded] 
 element.style  { ()
 
 [expanded] 
+#testDiv, my-custom-tag  { (inspector-stylesheet:1 -> inspector-stylesheet:1:1)
+
+[expanded] 
 #testDiv  { (style.css:1 -> style.css:1:1)
 color: green;
 
 [expanded] 
 div  { (user agent stylesheet)
 display: block;
 
 
 Opening front-end second time
 Dump styles after inspector was reopened:
 [expanded] 
 element.style  { ()
 
 [expanded] 
+#testdiv, my-custom-tag  { ()
+
+[expanded] 
 #testDiv  { (style.css:1 -> style.css:1:1)
 color: green;
 
 [expanded] 
 div  { (user agent stylesheet)
 display: block;