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..5f680e65bcbc90ae55ce25cc53384a079f98a861 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 +68,16 @@ const NSInteger CWVTranslationErrorScriptLoadError =
 @synthesize supportedLanguagesByCode = _supportedLanguagesByCode;
 @synthesize webState = _webState;
 
+#pragma mark - Class Methods
+
++ (void)resetTranslationPolicies {
+  ios_web_view::WebViewBrowserState* browserState =
+      [CWVWebViewConfiguration defaultConfiguration].browserState;

[michaeldo, 2017/07/07 18:16:01]

Sorry I didn't think of this before, but will this apply to other already
created and in use configurations? If not, we should explain in the method
comment that is will only apply to configurations created after it is called.

[Eugene But (OOO till 7-30), 2017/07/07 20:10:28]

What if clients want to reset policies for incognito configuration? Would it be
better to make |resetTranslationPolicies| instance method and pass prefs object
to TranslationController init?

[jzw1, 2017/07/08 01:09:41]

OK guys I've changed it so:
1. global instance for incognito and non-incognito browse states (2 total).
2. incognito browse state uses in memory store. 

this means translate preferences are not shared between incognito and
non-incognito.

[Eugene But (OOO till 7-30), 2017/07/10 16:17:43]

All methods related to translate policies are instance methods. Is there a
reason why only |reset| method is a class method? This looks inconsistent to me.

[jzw1, 2017/07/10 18:51:40]

The reason is because you can't get to an instance of CWVTranslationController
without having a CWVWebView, but you should still be able to clear translate
preferences without any existing CWVWebView. 

+  translate::TranslatePrefs translatePrefs(browserState->GetPrefs(),
+                                           prefs::kAcceptLanguages, nullptr);
+  translatePrefs.ResetToDefaults();
+}
+
 #pragma mark - Internal Methods
 
 - (void)setWebState:(web::WebState*)webState {