Expose method to reset translate settings.

ios/web_view/internal/translate/cwv_translation_controller.mm

Index: ios/web_view/internal/translate/cwv_translation_controller.mm
diff --git a/ios/web_view/internal/translate/cwv_translation_controller.mm b/ios/web_view/internal/translate/cwv_translation_controller.mm
index c62a8680ebdcd0ba3acbb29eda254f5df42185f6..17ed9e99831dac924f91ad294a7bd0d3526293d2 100644
--- a/ios/web_view/internal/translate/cwv_translation_controller.mm
+++ b/ios/web_view/internal/translate/cwv_translation_controller.mm
@@ -11,8 +11,11 @@
 #include "base/strings/sys_string_conversions.h"
 #include "components/translate/core/browser/translate_download_manager.h"
 #include "components/translate/core/browser/translate_manager.h"
+#import "ios/web_view/internal/cwv_web_view_configuration_internal.h"
+#include "ios/web_view/internal/pref_names.h"
 #import "ios/web_view/internal/translate/cwv_translation_language_internal.h"
 #import "ios/web_view/internal/translate/web_view_translate_client.h"
+#include "ios/web_view/internal/web_view_browser_state.h"
 #import "ios/web_view/public/cwv_translation_controller_delegate.h"
 #import "ios/web_view/public/cwv_translation_policy.h"
 #include "ui/base/l10n/l10n_util.h"
@@ -65,6 +68,17 @@ const NSInteger CWVTranslationErrorScriptLoadError =
 @synthesize supportedLanguagesByCode = _supportedLanguagesByCode;
 @synthesize webState = _webState;
 
+#pragma mark - Class Methods
+
++ (void)resetTranslationPolicies {
+  CWVWebViewConfiguration* configuration =
+      [CWVWebViewConfiguration defaultConfiguration];
+  PrefService* prefService = configuration.browserState->GetPrefs();
+  translate::TranslatePrefs translatePrefs(prefService, prefs::kAcceptLanguages,
+                                           nullptr);
+  translatePrefs.ResetToDefaults();
+}
+
 #pragma mark - Internal Methods
 
 - (void)setWebState:(web::WebState*)webState {
@@ -155,6 +169,7 @@ const NSInteger CWVTranslationErrorScriptLoadError =
 
 - (void)setTranslationPolicy:(CWVTranslationPolicy*)policy
              forPageLanguage:(CWVTranslationLanguage*)pageLanguage {
+  DCHECK(!_webState->GetBrowserState()->IsOffTheRecord());
   std::string languageCode = base::SysNSStringToUTF8(pageLanguage.languageCode);
   switch (policy.type) {
     case CWVTranslationPolicyAsk: {
@@ -198,6 +213,7 @@ const NSInteger CWVTranslationErrorScriptLoadError =
 
 - (void)setTranslationPolicy:(CWVTranslationPolicy*)policy
                  forPageHost:(NSString*)pageHost {
+  DCHECK(!_webState->GetBrowserState()->IsOffTheRecord());
   DCHECK(pageHost.length);
   switch (policy.type) {
     case CWVTranslationPolicyAsk: {