[DevTools] Refactor CSS live locations.

third_party/WebKit/Source/devtools/front_end/bindings/SASSSourceMapping.js

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 84 matching lines @@
         uiSourceCode.setWorkingCopy(sassText);
       }
     }
   }
 
   /**
    * @param {!SDK.CSSLocation} rawLocation
    * @return {?Workspace.UILocation}
    */
   rawLocationToUILocation(rawLocation) {
-    var sourceMap = this._cssModel.sourceMapForHeader(rawLocation.header());
+    var header = rawLocation.header();
+    if (!header)
+      return null;
+    var sourceMap = this._cssModel.sourceMapForHeader(header);
     if (!sourceMap)
       return null;
     var entry = sourceMap.findEntry(rawLocation.lineNumber, rawLocation.columnNumber);
     if (!entry || !entry.sourceURL)
       return null;
-    var uiSourceCode =
-        Bindings.NetworkProject.uiSourceCodeForStyleURL(this._workspace, entry.sourceURL, rawLocation.header());
+    var uiSourceCode = Bindings.NetworkProject.uiSourceCodeForStyleURL(this._workspace, entry.sourceURL, header);
     if (!uiSourceCode)
       return null;
     return uiSourceCode.uiLocation(entry.sourceLineNumber || 0, entry.sourceColumnNumber);
   }
 
   dispose() {
     Common.EventTarget.removeEventListeners(this._eventListeners);
   }
 };