WIP: Redirect .onion URLs to a private window with Tor, if possible.

fix brave/brave-browser#806

- If there is no private window with Tor open, fail.

  => TODO: This should fail noisily, beyond a console message.

  => One may be tempted to just create a private window with Tor, but:
     . This is not obviously easy to do here.
     . Users may not be happy if simply clicking a link can have the
       effect of using Tor when they didn't intend.

- If there is a private window with Tor open, create a new tab to load
  the page.

  => User expectations around onion services are likely to be that
     they provide anonymity, so opening them in the non-anonymous
     window may be surprising.

  => It is not clear how easy it would be to load in a non-Tor window
     and ensure that everything is nevertheless loaded through Tor --
     and likewise links from it, &c.

chromium_src/chrome/browser/ui/browser_navigator.cc

@@ -3,19 +3,39 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this file,
  * You can obtain one at http://mozilla.org/MPL/2.0/. */
 
+#include "brave/browser/profiles/brave_profile_manager.h"
 #include "brave/browser/renderer_host/brave_navigation_ui_data.h"
 #include "brave/common/webui_url_constants.h"
+#include "chrome/browser/browser_process.h"
+#include "chrome/browser/ui/browser_finder.h"
 #include "chrome/browser/ui/browser_navigator_params.h"
 #include "chrome/common/webui_url_constants.h"
 #include "url/gurl.h"
 
 namespace {
-void AdjustNavigateParamsForURLBraveImpl(NavigateParams* params) {
+bool AdjustNavigateParamsForURLBraveImpl(NavigateParams* params) {
   if (params->url.SchemeIs(content::kBraveUIScheme)) {
     GURL::Replacements replacements;
     replacements.SetSchemeStr(content::kChromeUIScheme);
     params->url = params->url.ReplaceComponents(replacements);
   }
+  if (params->url.SchemeIsHTTPOrHTTPS() &&
+      params->url.DomainIs("onion")) {
+    ProfileManager* profile_manager = g_browser_process->profile_manager();
+    Profile* profile = profile_manager->GetProfileByPath(
+        BraveProfileManager::GetTorProfilePath());
+    if (profile) {
+      Browser* browser = chrome::FindTabbedBrowser(profile, true);
+      DCHECK(browser);
+      params->disposition = WindowOpenDisposition::SINGLETON_TAB;
+      params->browser = browser;
+      params->window_action = NavigateParams::SHOW_WINDOW;
+    } else {
+      LOG(ERROR) << "Tried to load .onion without Tor ready";
+      return false;
+    }
+  }
+  return true;
 }
 
 bool IsHostAllowedInIncognitoBraveImpl(const base::StringPiece& host) {

patches/chrome-browser-ui-browser_navigator.cc.patch

@@ -1,16 +1,17 @@
 diff --git a/chrome/browser/ui/browser_navigator.cc b/chrome/browser/ui/browser_navigator.cc
-index 923eb172b0fcfd9f396f30cce4dc91593960056e..10d6e15e608927bf0c88ba034e3180fd0679acb6 100644
+index 923eb172b0fcfd9f396f30cce4dc91593960056e..639380ee99fb3b2fb46c6a74f7901e2e931e8a8c 100644
 --- a/chrome/browser/ui/browser_navigator.cc
 +++ b/chrome/browser/ui/browser_navigator.cc
-@@ -104,6 +104,7 @@ Browser* GetOrCreateBrowser(Profile* profile, bool user_gesture) {
+@@ -104,6 +104,8 @@ Browser* GetOrCreateBrowser(Profile* profile, bool user_gesture) {
  // Returns true on success. Otherwise, if changing params leads the browser into
  // an erroneous state, returns false.
  bool AdjustNavigateParamsForURL(NavigateParams* params) {
-+  AdjustNavigateParamsForURLBraveImpl(params);
++  if (!AdjustNavigateParamsForURLBraveImpl(params))
++    return false;
    if (params->contents_to_insert || params->switch_to_singleton_tab ||
        IsURLAllowedInIncognito(params->url, params->initiating_profile) ||
        params->initiating_profile->IsGuestSession()) {
-@@ -717,6 +718,7 @@ void Navigate(NavigateParams* params) {
+@@ -717,6 +719,7 @@ void Navigate(NavigateParams* params) {
  bool IsHostAllowedInIncognito(const GURL& url) {
    std::string scheme = url.scheme();
    base::StringPiece host = url.host_piece();