Add setting to isolate zoom changes by default.

chrome/browser/resources/options/content_settings.css

 /* Copyright (c) 2012 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. */
 
 #content-settings-page {
   min-width: 620px;
 }
 
 #content-settings-exceptions-area {
   min-width: 540px;
@@ skipping 39 matching lines @@
 }
 
 #exception-pattern-column {
   -webkit-box-flex: 1;
 }
 
 .exception-value-column-header {
   width: 145px;
 }
 
-.otr-explanation {
+.otr-explanation,
+#zoom-levels-ignored-explanation {
   font-style: italic;
 }
 
 #content-settings-exceptions-area list {
   margin-bottom: 10px;
   margin-top: 4px;
 }
 
 #group-indicator {
   margin-left: 5px;
@@ skipping 37 matching lines @@
   display: -webkit-box;
 }
 
 #media-audio-column {
   width: 6em;
 }
 
 #media-video-column {
   width: 8.5em;
 }