Restore thread check in KeyedService factories.

components/keyed_service/ios/browser_state_keyed_service_factory.cc

Index: components/keyed_service/ios/browser_state_keyed_service_factory.cc
diff --git a/components/keyed_service/ios/browser_state_keyed_service_factory.cc b/components/keyed_service/ios/browser_state_keyed_service_factory.cc
index 105e6992ce4b7a681dbe3a44c9d363d8cc9b8051..1651839b86be5a1af163fa420168042e1f2437ad 100644
--- a/components/keyed_service/ios/browser_state_keyed_service_factory.cc
+++ b/components/keyed_service/ios/browser_state_keyed_service_factory.cc
@@ -42,9 +42,6 @@ KeyedService* BrowserStateKeyedServiceFactory::GetServiceForBrowserState(
 
 web::BrowserState* BrowserStateKeyedServiceFactory::GetBrowserStateToUse(
     web::BrowserState* context) const {
-  // TODO(crbug.com/701326): This DCHECK should be moved to GetContextToUse().
-  DCHECK(CalledOnValidThread());
-
   // Safe default for Incognito mode: no service.
   if (context->IsOffTheRecord())
     return nullptr;
@@ -83,6 +80,7 @@ bool BrowserStateKeyedServiceFactory::IsOffTheRecord(
 
 base::SupportsUserData* BrowserStateKeyedServiceFactory::GetContextToUse(
     base::SupportsUserData* context) const {
+  DCHECK(CalledOnValidThread());
   AssertContextWasntDestroyed(context);
   return GetBrowserStateToUse(static_cast<web::BrowserState*>(context));
 }