Expose way to enable/disable translate.

ios/web_view/internal/cwv_preferences_internal.h

Index: ios/web_view/internal/cwv_preferences_internal.h
diff --git a/ios/web_view/internal/cwv_preferences_internal.h b/ios/web_view/internal/cwv_preferences_internal.h
new file mode 100644
index 0000000000000000000000000000000000000000..fa6681ad8a2995d6f8aac44ddf8abd0d8f045cf1
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+++ b/ios/web_view/internal/cwv_preferences_internal.h
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+// 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_INTERNAL_CWV_PREFERENCES_INTERNAL_H_
+#define IOS_WEB_VIEW_INTERNAL_CWV_PREFERENCES_INTERNAL_H_
+
+#import "ios/web_view/public/cwv_preferences.h"
+
+class PrefService;
+
+@interface CWVPreferences ()
+
+// Takes a PrefService object used to modify settings.
+// Caller must ensure |prefService| outlives this instance.
+- (instancetype)initWithPrefService:(PrefService*)prefService
+    NS_DESIGNATED_INITIALIZER;
+
+@end
+
+#endif  // IOS_WEB_VIEW_INTERNAL_CWV_PREFERENCES_INTERNAL_H_