Add gn implementation for //components/history/ios/browser.

components/history/ios/browser/BUILD.gn

Index: components/history/ios/browser/BUILD.gn
diff --git a/components/security_interstitials/core/BUILD.gn b/components/history/ios/browser/BUILD.gn
similarity index 53%
copy from components/security_interstitials/core/BUILD.gn
copy to components/history/ios/browser/BUILD.gn
index d60bad3646cef3be59a89f8717da1fdb4e4d3bb2..960d778a0e6a938c5b8bfa584656ce6f48093964 100644
--- a/components/security_interstitials/core/BUILD.gn
+++ b/components/history/ios/browser/BUILD.gn
@@ -2,18 +2,18 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-# GYP version: components/security_interstitials.gyp:security_interstitials_core
-static_library("core") {
+source_set("browser") {
   sources = [
-    "metrics_helper.cc",
-    "metrics_helper.h",
+    "history_database_helper.cc",
+    "history_database_helper.h",
+    "web_state_top_sites_observer.cc",
+    "web_state_top_sites_observer.h",
   ]
 
   deps = [
     "//base",
     "//components/history/core/browser",
-    "//components/metrics",
-    "//components/rappor",
-    "//net",
+    "//ios/web",
+    "//url",
   ]
 }