DevTools: automatic mapping detection is broken for cases with specific file paths.

third_party/WebKit/Source/devtools/front_end/workspace/FileSystemMapping.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 293 matching lines @@
     {
         var commonPathSuffixLength = 0;
         for (var i = 0; i < filePath.length; ++i) {
             var filePathCharacter = filePath[filePath.length - 1 - i];
             var urlCharacter = url[url.length - 1 - i];
             if (filePathCharacter !== urlCharacter)
                 break;
             if (filePathCharacter === "/")
                 commonPathSuffixLength = i;
         }
-        var pathPrefix = filePath.substring(fileSystemPath.length, filePath.length - commonPathSuffixLength);
+        var from = fileSystemPath.length;
+        var to = filePath.length - commonPathSuffixLength;
+        var pathPrefix = filePath.substring(from, to);
         var urlPrefix = url.substr(0, url.length - commonPathSuffixLength);
-        this.addFileMapping(fileSystemPath, urlPrefix, pathPrefix);
+        if (to >= from)
+            this.addFileMapping(fileSystemPath, urlPrefix, pathPrefix);
+        else
+            this.addFileMapping(fileSystemPath, urlPrefix + pathPrefix, "/");
     },
 
     resetForTesting: function()
     {
         this._fileSystemMappings = {};
     },
 
     __proto__: WebInspector.Object.prototype
 }
 
 /**
  * @constructor
  * @param {string} fileSystemPath
  * @param {string} urlPrefix
  * @param {string} pathPrefix
  * @param {boolean} configurable
  */
 WebInspector.FileSystemMapping.Entry = function(fileSystemPath, urlPrefix, pathPrefix, configurable)
 {
     this.fileSystemPath = fileSystemPath;
     this.urlPrefix = urlPrefix;
     this.pathPrefix = pathPrefix;
     this.configurable = configurable;
 }
 
 /**
  * @type {!WebInspector.FileSystemMapping}
  */
 WebInspector.fileSystemMapping;