Expose method to reset translate settings.

ios/web_view/internal/cwv_web_view_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_web_view_configuration.h"
 #import "ios/web_view/internal/cwv_web_view_configuration_internal.h"
 
 #include "base/memory/ptr_util.h"
 #include "base/threading/thread_restrictions.h"
-#include "components/translate/core/browser/translate_download_manager.h"
 #include "ios/web_view/internal/app/application_context.h"
 #import "ios/web_view/internal/cwv_user_content_controller_internal.h"
 #include "ios/web_view/internal/web_view_browser_state.h"
 #include "ios/web_view/internal/web_view_global_state_util.h"
 
 #if !defined(__has_feature) || !__has_feature(objc_arc)
 #error "This file requires ARC support."
 #endif
 
 @interface CWVWebViewConfiguration () {
   // The BrowserState for this configuration.
   std::unique_ptr<ios_web_view::WebViewBrowserState> _browserState;
 }
 
 // Initializes configuration with the specified browser state mode.
 - (instancetype)initWithBrowserState:
     (std::unique_ptr<ios_web_view::WebViewBrowserState>)browserState;
 @end
 
 @implementation CWVWebViewConfiguration
 
 @synthesize userContentController = _userContentController;
 
 + (instancetype)defaultConfiguration {
-  auto browserState =
-      base::MakeUnique<ios_web_view::WebViewBrowserState>(false);
-  return [[self alloc] initWithBrowserState:std::move(browserState)];
+  static CWVWebViewConfiguration* defaultConfiguration;
+  static dispatch_once_t onceToken;
+  dispatch_once(&onceToken, ^{
+    auto browserState =
+        base::MakeUnique<ios_web_view::WebViewBrowserState>(false);
+    defaultConfiguration =
+        [[self alloc] initWithBrowserState:std::move(browserState)];
+  });
+  return defaultConfiguration;
 }
 
 + (instancetype)incognitoConfiguration {
-  auto browserState = base::MakeUnique<ios_web_view::WebViewBrowserState>(true);
-  return [[self alloc] initWithBrowserState:std::move(browserState)];
+  static CWVWebViewConfiguration* incognitoConfiguration;
+  static dispatch_once_t onceToken;
+  dispatch_once(&onceToken, ^{
+    auto browserState =
+        base::MakeUnique<ios_web_view::WebViewBrowserState>(true);
+    incognitoConfiguration =
+        [[self alloc] initWithBrowserState:std::move(browserState)];
+  });
+  return incognitoConfiguration;
 }
 
 + (void)initialize {
   if (self != [CWVWebViewConfiguration class]) {
     return;
   }
 
   ios_web_view::InitializeGlobalState();
 }
 
 - (instancetype)initWithBrowserState:
     (std::unique_ptr<ios_web_view::WebViewBrowserState>)browserState {
   self = [super init];
   if (self) {
     _browserState = std::move(browserState);
 
     _userContentController =
         [[CWVUserContentController alloc] initWithConfiguration:self];
   }
   return self;
 }
 
+#pragma mark - Public Methods
+
 - (BOOL)isPersistent {
   return !_browserState->IsOffTheRecord();
 }
 
+#pragma mark - Private Methods
+
 - (ios_web_view::WebViewBrowserState*)browserState {
   return _browserState.get();
 }
 
 @end