Split //ios/chrome/browser in multiple targets.

ios/chrome/browser/undo/BUILD.gn

Index: ios/chrome/browser/undo/BUILD.gn
diff --git a/components/physical_web/webui/BUILD.gn b/ios/chrome/browser/undo/BUILD.gn
similarity index 50%
copy from components/physical_web/webui/BUILD.gn
copy to ios/chrome/browser/undo/BUILD.gn
index f3d6432dd2b700c0f266293e7ce3eef7ca158809..d2dcc71c82a019a15fd373796e554aaef0750107 100644
--- a/components/physical_web/webui/BUILD.gn
+++ b/ios/chrome/browser/undo/BUILD.gn
@@ -2,13 +2,15 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-source_set("webui") {
+source_set("undo") {
   sources = [
-    "physical_web_ui_constants.cc",
-    "physical_web_ui_constants.h",
+    "bookmark_undo_service_factory.cc",
+    "bookmark_undo_service_factory.h",
   ]
-
   deps = [
     "//base",
+    "//components/keyed_service/ios",
+    "//components/undo",
+    "//ios/chrome/browser/browser_state",
   ]
 }