[ios] Use chrome_browser_state_forward.h in /ios/chrome/browser/sync/consent_auditor_factory.h

Instead of forward declaring ChromeBrowserState in the ios
namespace, use a header. This will allow moving the class
to the global namespace without having to change all the
forward declaration at the same time.

This CL was uploaded by git cl split.

R=msarda@chromium.org

Bug: 1042208
Change-Id: I5e7941be37469d17ae0610fb475ae10533cd79f4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2010788
Auto-Submit: Sylvain Defresne <sdefresne@chromium.org>
Reviewed-by: Mihai Sardarescu <msarda@chromium.org>
Commit-Queue: Sylvain Defresne <sdefresne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#733425}

ios/chrome/browser/sync/consent_auditor_factory.h

@@ -13,15 +13,12 @@
 #include "base/macros.h"
 #include "base/no_destructor.h"
 #include "components/keyed_service/ios/browser_state_keyed_service_factory.h"
+#include "ios/chrome/browser/browser_state/chrome_browser_state_forward.h"
 
 namespace consent_auditor {
 class ConsentAuditor;
 }  // namespace consent_auditor
 
-namespace ios {
-class ChromeBrowserState;
-}  // namespace ios
-
 // Singleton that owns all ConsentAuditors and associates them with
 // ios::ChromeBrowserState.
 class ConsentAuditorFactory : public BrowserStateKeyedServiceFactory {