Add support for a "split" incognito behavior for extensions.

chrome/common/extensions/docs/experimental.sidebar.html

Index: chrome/common/extensions/docs/experimental.sidebar.html
diff --git a/chrome/common/extensions/docs/experimental.sidebar.html b/chrome/common/extensions/docs/experimental.sidebar.html
index 9e19c3454c046de7ff73651315023aeccf1070a5..e4983a3b1d0074a5f8c5e7c9d8c6cb26c1361959 100644
--- a/chrome/common/extensions/docs/experimental.sidebar.html
+++ b/chrome/common/extensions/docs/experimental.sidebar.html
@@ -937,7 +937,7 @@
           <dd class="todo" style="display: none; ">
             Undocumented.
           </dd>
-          <dd>'hidden' indicates sidebar is not defined for the specified tab (show was never called or hide() was called). Nothing is displayed for this sidebar.'shown' means sidebar is defined for the specified tab; mini tab is displayed for this sidebar. Sidebar UI is either collapsed or displaying a content of some other extension's sidebar.'active' indicates that sidebar is defined for the specified tab; sidebar UI is expanded and displaying this sidebar's content.</dd>
+          <dd>'hidden' indicates sidebar is not defined for the specified tab (show was never called or hide() was called). Nothing is displayed for this sidebar.<br>'shown' means sidebar is defined for the specified tab; mini tab is displayed for this sidebar. Sidebar UI is either collapsed or displaying a content of some other extension's sidebar.<br>'active' indicates that sidebar is defined for the specified tab; sidebar UI is expanded and displaying this sidebar's content.</dd>
           <dd style="display: none; ">
             This parameter was added in version
             <b><span></span></b>.