DevTools: Remove unused variables. Disallow unused variables with eslint

third_party/WebKit/Source/devtools/front_end/source_frame/SourcesTextEditor.js

 // Copyright (c) 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 /**
  * @unrestricted
  */
 SourceFrame.SourcesTextEditor = class extends TextEditor.CodeMirrorTextEditor {
   /**
    * @param {!SourceFrame.SourcesTextEditorDelegate} delegate
    */
@@ skipping 523 matching lines @@
   _trailingWhitespaceOverlayMode(mimeType) {
     var modeName = CodeMirror.mimeModes[mimeType] ?
         (CodeMirror.mimeModes[mimeType].name || CodeMirror.mimeModes[mimeType]) :
         CodeMirror.mimeModes['text/plain'];
     modeName += '+trailing-whitespaces';
     if (CodeMirror.modes[modeName])
       return modeName;
 
     function modeConstructor(config, parserConfig) {
       function nextToken(stream) {
-        var pos = stream.pos;
         if (stream.match(/^\s+$/, true))
           return true ? 'trailing-whitespace' : null;
         do
           stream.next();
         while (!stream.eol() && stream.peek() !== ' ');
         return null;
       }
       var whitespaceMode = {token: nextToken};
       return CodeMirror.overlayMode(CodeMirror.getMode(config, mimeType), whitespaceMode, false);
     }
@@ skipping 316 matching lines @@
    */
   _setHighlighter(highlighter, selectionStart) {
     var overlayMode = {token: highlighter};
     this._codeMirror.addOverlay(overlayMode);
     this._highlightDescriptor = {overlay: overlayMode, selectionStart: selectionStart};
   }
 };
 
 SourceFrame.SourcesTextEditor.LinesToScanForIndentationGuessing = 1000;
 SourceFrame.SourcesTextEditor.MaximumNumberOfWhitespacesPerSingleSpan = 16;