Add a message to empty ContentSuggestions sections

ios/chrome/browser/ui/content_suggestions/BUILD.gn

Index: ios/chrome/browser/ui/content_suggestions/BUILD.gn
diff --git a/ios/chrome/browser/ui/content_suggestions/BUILD.gn b/ios/chrome/browser/ui/content_suggestions/BUILD.gn
index 1334fccec4ee6f6761fafcc770cd87f68ad64c52..0d17e38a5b8cda06ffeb84af0f5e520bdd2b4cab 100644
--- a/ios/chrome/browser/ui/content_suggestions/BUILD.gn
+++ b/ios/chrome/browser/ui/content_suggestions/BUILD.gn
@@ -17,6 +17,7 @@ source_set("content_suggestions") {
   ]
   deps = [
     "//base",
+    "//components/strings",
     "//ios/chrome/browser/ui/collection_view",
     "//ios/chrome/browser/ui/content_suggestions/cells",
     "//ios/chrome/browser/ui/content_suggestions/identifier",
@@ -28,3 +29,19 @@ source_set("content_suggestions") {
   ]
   configs += [ "//build/config/compiler:enable_arc" ]
 }
+
+source_set("unit_tests") {
+  testonly = true
+  sources = [
+    "content_suggestions_collection_updater_unittest.mm",
+  ]
+  deps = [
+    ":content_suggestions",
+    "//base",
+    "//ios/chrome/browser/ui/collection_view",
+    "//ios/chrome/browser/ui/content_suggestions/identifier",
+    "//testing/gtest",
+    "//third_party/ocmock",
+  ]
+  configs += [ "//build/config/compiler:enable_arc" ]
+}