[268]thread_restrictions: Add PermissionManagerQt as friend class

This is needed for the addition of permission persistence, which
requires serializing to disk.

Change-Id: Idf9d310535c28e77744b94a0f44b726d1f55d6a6
Reviewed-on: https://codereview.qt-project.org/c/qt/qtwebengine-chromium/+/549638
Reviewed-by: Michael Brüning <michael.bruning@qt.io>
(cherry picked from commit f3033f5)
Reviewed-on: https://codereview.qt-project.org/c/qt/qtwebengine-chromium/+/564886
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>

Author: Kaloyan Chehlarski

chromium/base/threading/thread_restrictions.h

@@ -460,6 +460,7 @@ namespace QtWebEngineCore {
 class DevToolsFrontendQt;
 class PrefServiceAdapter;
 class ProfileAdapter;
+class PermissionManagerQt;
 }
 
 namespace base {
@@ -673,6 +674,7 @@ class BASE_EXPORT ScopedAllowBlocking {
   friend class QtWebEngineCore::DevToolsFrontendQt;
   friend class QtWebEngineCore::PrefServiceAdapter;
   friend class QtWebEngineCore::ProfileAdapter;
+  friend class QtWebEngineCore::PermissionManagerQt;
 
   // Sorted by function name (with namespace), ignoring the return type.
   friend Profile* ::GetLastProfileMac();  // http://crbug.com/1176734