DevTools: Provide #sourceURL for CSS stylesheets in the debug_devtools=1 mode

Source/devtools/front_end/Runtime.js

 /*
  * Copyright (C) 2014 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 663 matching lines @@
         /**
          * @param {string} path
          * @param {string=} content
          */
         function cacheStylesheet(path, content)
         {
             if (!content) {
                 console.error("Failed to load stylesheet: " + path);
                 return;
             }
-            Runtime.cachedResources[path] = content;
+            var sourceURL = window.location.href;
+            if (window.location.search)
+                sourceURL.replace(window.location.search, "");
+            sourceURL = sourceURL.substring(0, sourceURL.lastIndexOf("/") + 1) + path;
+            Runtime.cachedResources[path] = content + "\n/*# sourceURL=" + sourceURL + " */";
         }
     },
 
     /**
      * @return {!Promise.<undefined>}
      */
     _loadScripts: function()
     {
         if (!this._descriptor.scripts)
             return Promise.resolve();
@@ skipping 296 matching lines @@
         }
     }
 })();}
 
 
 // This must be constructed after the query parameters have been parsed.
 Runtime.experiments = new Runtime.ExperimentsSupport();
 
 /** @type {!Runtime} */
 var runtime;