4 spaces for tab size in view source.

third_party/WebKit/Source/core/css/view-source.css

 /*
  * Copyright (C) 2006 Apple Computer, 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
  *
  * THIS SOFTWARE IS PROVIDED BY APPLE COMPUTER, INC. ``AS IS'' AND ANY
  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE COMPUTER, INC. OR
  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
  * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
- * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 body {
     margin: 0
 }
 
 table {
     width: 100%;
     border-spacing: 0;
     white-space: pre-wrap !important;
     margin: 0;
     word-break: break-word;
     font-size: initial;
     font-family: monospace;
+    tab-size: 4;
 }
 
 td {
     padding: 0 !important;
     vertical-align: baseline
 }
 
 .line-gutter-backdrop, .line-number {
     /* Keep this in sync with inspector.css (.webkit-line-gutter-backdrop) */
     box-sizing: border-box;
@@ skipping 78 matching lines @@
 .html-doctype {
     /* Keep this in sync with inspectorSyntaxHighlight.css (.webkit-html-doctype) */
     color: rgb(192, 192, 192);
 }
 
 .html-end-of-file {
     /* Keep this in sync with inspectorSyntaxHighlight.css (.webkit-html-end-of-file) */
     color: rgb(255, 0, 0);
     font-weight: bold;
 }