[ios] Implemented iOS analogue of SSLErrorHandler class.

ios/chrome/browser/ssl/ios_ssl_error_handler.h

+// Copyright 2016 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_CHROME_BROWSER_SSL_IOS_SSL_ERROR_HANDLER_H_
+#define IOS_CHROME_BROWSER_SSL_IOS_SSL_ERROR_HANDLER_H_
+
+#include "base/callback.h"
+#include "url/gurl.h"
+
+namespace net {
+class SSLInfo;
+}  // namespace net
+
+namespace web {
+class WebState;
+}  // namespace web
+
+// This class is responsible for deciding what type of interstitial to show for
+// an SSL validation error.
+class IOSSSLErrorHandler {
+ public:
+  // Entry point for the class.
+  static void HandleSSLError(web::WebState* web_state,

[estark, 2016/06/29 23:00:15]

I'm not sure what the prevailing style is on ios, but in normal Chrome code I'd
say it's a little weird to have a class that just has two static methods. Could
you perhaps just make these standalone functions instead?

[Eugene But (OOO till 7-30), 2016/06/30 00:05:26]

No it's not prevailing style on iOS, and I do agree that a class with just
static functions can just be replaced with namespaced static functions. 
My goal was to mirror chrome, which has SSLErrorHandler class with 4 static
public functions (and I would argue that it could also be implemented as 4
namespaced functions).

Currently IOSSSLErrorHandler does not have much meat in the implementation, but
it will grow as we add more features (i.e. captive portal support). So unless
you have strong opinion, I would leave this weird class as it is with a single
static method. Please let me know if you disagree.

[estark, 2016/06/30 17:02:04]

SSLErrorHandler has non-static protected/private methods though and is
constructed from one of the static methods. But that seems fine to leave it as
is if you think it'll grow.

+                             int cert_error,
+                             const net::SSLInfo& info,
+                             const GURL& request_url,
+                             bool overridable,
+                             const base::Callback<void(bool)>& callback);
+
+ private:
+  IOSSSLErrorHandler();
+  ~IOSSSLErrorHandler();
+  // Called on SSL interstitial dismissal.
+  static void InterstitialWasDismissed(
+      web::WebState* web_state,
+      const base::Callback<void(bool)>& callback,
+      bool proceed);
+};
+
+#endif  // IOS_CHROME_BROWSER_SSL_IOS_SSL_ERROR_HANDLER_H_