Block loading .onion sites in non-Tor tabs.

fix #14431

Auditors: @diracdeltas @bsclifton

Test Plan:
I:	1. Open a tab _without_ Tor (private or nonprivate).
	2. Enter https://nyttips4bmquxfzw.onion/.
	3. Confirm that Brave blocks loading the URL.

II:	1. Open a private tab with Tor.
	2. Enter https://nyttips4bmquxfzw.onion/.
	3. Confirm that the NYT SecureDrop page loads.
	4. Bookmark it.
	5. Open a tab _without_ Tor (private or nonprivate).
	6. Try to load the bookmark.
	7. Confirm that Brave blocks loading the bookmark.

app/extensions/brave/locales/en-US/app.properties

@@ -238,6 +238,7 @@ submit=Submit
 tabsSuggestionTitle=Tabs
 topSiteSuggestionTitle=Top Site
 urlBlockedInTor=For your privacy, Brave blocks this URL from loading in a private tab when Tor is enabled.
+urlBlockedOutsideTor=For your privacy, Brave blocks this URL from loading in a tab without Tor.
 urlWarningOk=Ok
 torConnectionError=Unable to connect to the Tor network
 torConnectionErrorInfo=Brave could not make a connection to the Tor network. Disable Tor to continue private browsing without Tor protection.

app/filtering.js

@@ -130,6 +130,14 @@ function registerForBeforeRequest (session, partition) {
         onBlockedInTor(details, muonCb)
         return
       }
+    } else {
+      const host = urlParse(details.url).host
+      // US-ASCII only in `.onion', so no need for locale-dependent
+      // case-insensitive comparisons.
+      if (host.toLowerCase().endsWith('.onion')) {
+        onBlockedOutsideTor(details, muonCb)
+        return
+      }
     }
 
     if (process.env.NODE_ENV === 'development') {
@@ -406,6 +414,19 @@ function onBlockedInTor (details, muonCb) {
   }
 }
 
+function onBlockedOutsideTor (details, muonCb) {
+  const cb = () => muonCb({cancel: true})
+  if (details.tabId && details.resourceType === 'mainFrame') {
+    tabMessageBox.show(details.tabId, {
+      message: `${locale.translation('urlBlockedOutsideTor')}`,
+      title: 'Brave',
+      buttons: [locale.translation('urlWarningOk')]
+    }, cb)
+  } else {
+    cb()
+  }
+}
+
 /**
  * Register for notifications for webRequest.onHeadersReceived for a particular
  * session.

app/locale.js

@@ -270,6 +270,7 @@ var rendererIdentifiers = function () {
     'noDownloads',
     'torrentDesc',
     'urlBlockedInTor',
+    'urlBlockedOutsideTor',
     'urlWarningOk',
     'multiSelectionBookmarks',
     // Caption buttons in titlebar (min/max/close - Windows only)