Expose way to enable/disable translate.

ios/web_view/public/cwv_preferences.h

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef IOS_WEB_VIEW_PUBLIC_CWV_PREFERENCES_H_
+#define IOS_WEB_VIEW_PUBLIC_CWV_PREFERENCES_H_
+
+#import <Foundation/Foundation.h>
+
+#import "cwv_export.h"
+
+// Preferences for user settings.
+CWV_EXPORT
+@interface CWVPreferences : NSObject
+
+// Whether or not translation as a feature is turned on.
+@property(nonatomic, assign, getter=isTranslationEnabled)
+    BOOL translationEnabled;
+
+- (instancetype)init NS_UNAVAILABLE;
+
+// Resets all translation settings back to default. In particular, this will
+// change all translation policies back to CWVTranslationPolicyAsk.
+- (void)resetTranslationSettings;
+
+@end
+
+#endif  // IOS_WEB_VIEW_PUBLIC_CWV_PREFERENCES_H_