Extension - Docs - Add a note where user cannot override newtab incognito windows.

Since new tab pages cannot be overridden in incognito windows, a note should be specified in the documentation. Some users I have seen in IRC and Forums have this confusion.

The reason why you cannot override is from the following bug, where extension developers discussed the following issue:
http://crbug.com/39372

BUG=None
TEST=Open the page and the content will be shown

Review URL: http://codereview.chromium.org/6295008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@72286 0039d316-1c4b-4281-b951-d872f2087c98

chrome/common/extensions/docs/override.html

@@ -388,6 +388,11 @@ specify "spanning" mode for the <a href="manifest.html#incognito">incognito</a>
 manifest property.
 </p>
 
+<p class="note">
+<b>Note:</b>
+You cannot override the New Tab page in incognito windows.
+</p>
+
 <p>
 The following screenshots show the default New Tab page
 next to a custom New Tab page.

chrome/common/extensions/docs/static/override.html

@@ -70,6 +70,11 @@ specify "spanning" mode for the <a href="manifest.html#incognito">incognito</a>
 manifest property.
 </p>
 
+<p class="note">
+<b>Note:</b>
+You cannot override the New Tab page in incognito windows.
+</p>
+
 <p>
 The following screenshots show the default New Tab page
 next to a custom New Tab page.