Expose way to enable/disable translate.

ios/web_view/internal/translate/cwv_translation_configuration.mm

+// 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.
+
+#import "ios/web_view/public/cwv_translation_configuration.h"
+#import "ios/web_view/internal/translate/cwv_translation_configuration_internal.h"
+
+#include "components/prefs/pref_service.h"
+#include "components/translate/core/browser/translate_pref_names.h"
+#include "components/translate/core/browser/translate_prefs.h"
+#include "ios/web_view/internal/pref_names.h"
+
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
+@implementation CWVTranslationConfiguration {
+  PrefService* _prefService;
+}
+
+@dynamic enabled;
+
+- (instancetype)initWithPrefService:(PrefService*)prefService {
+  self = [super init];
+  if (self) {
+    _prefService = prefService;
+  }
+  return self;
+}
+
+#pragma mark - Public Methods
+
+- (void)setEnabled:(BOOL)enabled {
+  _prefService->SetBoolean(prefs::kEnableTranslate, enabled);
+}
+
+- (BOOL)enabled {
+  return _prefService->GetBoolean(prefs::kEnableTranslate);
+}
+
+- (void)reset {
+  translate::TranslatePrefs translatePrefs(_prefService,
+                                           prefs::kAcceptLanguages, nullptr);

[Eugene But (OOO till 7-30), 2017/07/14 00:22:42]

nit: Do you want to document nullptr with comments or using a local variable?

[jzw1, 2017/07/14 02:09:49]

I think it's OK to omit. The initializer in translate_prefs.h says:
  // |preferred_languages_pref| is only used on Chrome OS, other platforms must
  // pass NULL.

[Hiroshi Ichikawa, 2017/07/14 02:55:49]

No, it should be still commented. It can be like this:

  translate::TranslatePrefs translatePrefs(_prefService,
                                            prefs::kAcceptLanguages,
/*preferred_languages_pref=*/nullptr);

Otherwise people would wonder what this nullptr is. See "Function Argument
Comments" in:
https://google.github.io/styleguide/cppguide.html#Implementation_Comments

As a general rule, ideally, people should be able to understand the code without
referring to the definition of the classes/functions called from there.

+  translatePrefs.ResetToDefaults();
+}
+
+@end