Refactor creation of SadTabView into a tab helper object

ios/chrome/browser/web/BUILD.gn

Index: ios/chrome/browser/web/BUILD.gn
diff --git a/ios/chrome/browser/web/BUILD.gn b/ios/chrome/browser/web/BUILD.gn
index 6cd5023e0c1434e6016354d28d3d89ac53a502eb..739ebc83a85456419c82422ae0ae8ee64723ce49 100644
--- a/ios/chrome/browser/web/BUILD.gn
+++ b/ios/chrome/browser/web/BUILD.gn
@@ -15,12 +15,16 @@ source_set("web") {
     "network_activity_indicator_tab_helper.mm",
     "repost_form_tab_helper.h",
     "repost_form_tab_helper.mm",
+    "sad_tab_tab_helper.h",
+    "sad_tab_tab_helper.mm",
   ]
   deps = [
+    ":sad_tab_tab_helper_delegate",
     "//base",
     "//components/strings",
     "//ios/chrome/browser/ui",
     "//ios/chrome/browser/ui/alert_coordinator:alert_coordinator",
+    "//ios/chrome/browser/ui/sad_tab:sad_tab",
     "//ios/chrome/browser/ui/util:util",
     "//ios/web",
     "//ios/web:web_arc",
@@ -28,6 +32,13 @@ source_set("web") {
   ]
 }
 
+source_set("sad_tab_tab_helper_delegate") {
+  configs += [ "//build/config/compiler:enable_arc" ]
+  sources = [
+    "sad_tab_tab_helper_delegate.h",
+  ]
+}
+
 source_set("unit_tests") {
   configs += [ "//build/config/compiler:enable_arc" ]
   testonly = true
@@ -35,6 +46,7 @@ source_set("unit_tests") {
     "navigation_manager_util_unittest.mm",
     "network_activity_indicator_tab_helper_unittest.mm",
     "repost_form_tab_helper_unittest.mm",
+    "sad_tab_tab_helper_unittest.mm",
   ]
   deps = [
     ":web",