Add public API for handling Javascript alerts and prompt.

ios/web/BUILD.gn

 # Copyright 2015 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/build/config.gni")
 import("//ios/web/js_compile.gni")
 import("//testing/test.gni")
 import("//tools/grit/grit_rule.gni")
 
 source_set("web") {
@@ skipping 89 matching lines @@
     "public/browser_url_rewriter.h",
     "public/cert_policy.h",
     "public/cert_store.h",
     "public/certificate_policy_cache.h",
     "public/favicon_status.cc",
     "public/favicon_status.h",
     "public/favicon_url.cc",
     "public/favicon_url.h",
     "public/interstitials/web_interstitial.h",
     "public/interstitials/web_interstitial_delegate.h",
+    "public/java_script_dialog_callback.h",
+    "public/java_script_dialog_presenter.h",
+    "public/java_script_dialog_type.h",
     "public/load_committed_details.h",
     "public/navigation_item.h",
     "public/navigation_manager.h",
     "public/origin_util.h",
     "public/origin_util.mm",
     "public/referrer.h",
     "public/referrer_util.cc",
     "public/referrer_util.h",
     "public/security_style.h",
     "public/ssl_status.cc",
@@ skipping 437 matching lines @@
 }
 
 grit("resources") {
   source = "ios_web_resources.grd"
   use_qualified_include = true
   outputs = [
     "grit/ios_web_resources.h",
     "ios_web_resources.pak",
   ]
 }