Ensure the JavaScript world ID is set for Brave Ads

This fixes several upstream browser tests crashing on DCHECK-enabled
builds because of calls to dom_distiller::RunIsolatedJavaScript() being
run without the ID being previously set, with erros like this:

  [497557:497557:1221/135319.265636:FATAL:distiller_javascript_utils.cc(41)] Check failed: distiller_javascript_world_id != invalid_world_id.
  #0 0x7fd8cc5b7459 base::debug::CollectStackTrace()
  #1 0x7fd8cc4b12d3 base::debug::StackTrace::StackTrace()
  #2 0x7fd8cc4d3a34 logging::LogMessage::~LogMessage()
  #3 0x7fd8cc4d44ae logging::LogMessage::~LogMessage()
  #4 0x56550ee1de70 dom_distiller::RunIsolatedJavaScript()
  #5 0x56550fffc990 brave_ads::AdsTabHelper::RunIsolatedJavaScript()
  #6 0x7fd8c6332b3d content::WebContentsImpl::WebContentsObserverList::NotifyObservers<>()
  #7 0x7fd8c63531a9 content::WebContentsImpl::DocumentOnLoadCompleted()
  [...]
  #56 0x56550ccba27a _start
  Task trace:
  #0 0x7fd8c6c6ebee IPC::(anonymous namespace)::ChannelAssociatedGroupController::Accept()
  #1 0x7fd8cbce69df mojo::SimpleWatcher::Context::Notify()
  Crash keys:
    "ui_scheduler_async_stack" = "0x7FD8C6C6EBEE 0x7FD8CBCE69DF"
    "io_scheduler_async_stack" = "0x7FD8CBCE69DF 0x0"

  [1/1] TabStripBrowsertest.ShiftGroupLeft_OtherGroup (CRASHED)

browser/brave_ads/ads_tab_helper.cc

@@ -11,6 +11,7 @@
 #include "base/hash/hash.h"
 #include "brave/browser/brave_ads/ads_service_factory.h"
 #include "chrome/browser/profiles/profile.h"
+#include "chrome/common/chrome_isolated_world_ids.h"
 #include "components/dom_distiller/content/browser/distiller_javascript_utils.h"
 #include "components/dom_distiller/content/browser/distiller_page_web_contents.h"
 #include "components/sessions/content/session_tab_helper.h"
@@ -45,6 +46,11 @@ AdsTabHelper::AdsTabHelper(content::WebContents* web_contents)
   OnBrowserSetLastActive(BrowserList::GetInstance()->GetLastActive());
 #endif
   OnVisibilityChanged(web_contents->GetVisibility());
+
+  // Set the JavaScript world ID if not assigned yet.
+  if (!dom_distiller::DistillerJavaScriptWorldIdIsSet())
+    dom_distiller::SetDistillerJavaScriptWorldId(
+        ISOLATED_WORLD_ID_BRAVE_INTERNAL);
 }
 
 AdsTabHelper::~AdsTabHelper() {