Import CaptivePortalDetectorTabHelperDelegate for use in @protocol.

Bug: 875620
Cq-Include-Trybots: luci.chromium.try:ios-simulator-full-configs;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: I3ae27d80eb08915ae57a83d3c50b14cf4551874b
Reviewed-on: https://chromium-review.googlesource.com/1181687Reviewed-by: Eugene But <eugenebut@chromium.org>
Commit-Queue: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#584517}

ios/chrome/browser/ssl/ios_ssl_error_handler_unittest.mm

@@ -9,6 +9,7 @@
 #import "base/test/ios/wait_util.h"
 #include "ios/chrome/browser/browser_state/test_chrome_browser_state.h"
 #import "ios/chrome/browser/ssl/captive_portal_detector_tab_helper.h"
+#import "ios/chrome/browser/ssl/captive_portal_detector_tab_helper_delegate.h"
 #include "ios/web/public/interstitials/web_interstitial.h"
 #import "ios/web/public/test/web_test_with_web_state.h"
 #import "ios/web/public/web_state/web_state.h"