Register PrefsTabHelper for portals on Android.

This helper is responsible for propagating pref changes, and its
behavior is pretty nicely isolated to the WebContents it is attached to,
and so behaves fine across activation etc.

Fixed: 1086253
Change-Id: Iee77fc2d89706b1a217fac8a921eae44ecbdba44
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2215307
Auto-Submit: Jeremy Roman <jbroman@chromium.org>
Commit-Queue: Yaron Friedman <yfriedman@chromium.org>
Reviewed-by: Yaron Friedman <yfriedman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#771656}

chrome/browser/android/tab_web_contents_delegate_android.cc

@@ -46,6 +46,7 @@
 #include "chrome/browser/ui/blocked_content/popup_tracker.h"
 #include "chrome/browser/ui/browser_navigator_params.h"
 #include "chrome/browser/ui/interventions/framebust_block_message_delegate.h"
+#include "chrome/browser/ui/prefs/prefs_tab_helper.h"
 #include "chrome/browser/ui/tab_helpers.h"
 #include "chrome/browser/vr/vr_tab_helper.h"
 #include "chrome/common/chrome_switches.h"
@@ -159,6 +160,7 @@ void TabWebContentsDelegateAndroid::PortalWebContentsCreated(
       autofill::ChromeAutofillClient::FromWebContents(portal_contents));
   HistoryTabHelper::CreateForWebContents(portal_contents);
   InfoBarService::CreateForWebContents(portal_contents);
+  PrefsTabHelper::CreateForWebContents(portal_contents);
 }
 
 void TabWebContentsDelegateAndroid::RunFileChooser(