[iOS] Enabling Illustrated Empty States by default

This feature is launching to 95% soon. Enabling by default; cleanup CLs
to remove the flag will follow once that reaches 100%.

Bug: 1098328
Change-Id: Iac5c5aa8ba592c6785af0f5b1c1be4f6ea0303c0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2535876Reviewed-by: sebsg <sebsg@chromium.org>
Commit-Queue: Tommy Martino <tmartino@chromium.org>
Cr-Commit-Position: refs/heads/master@{#827367}

ios/chrome/browser/ui/ui_feature_flags.cc

@@ -52,7 +52,7 @@ const base::Feature kSafetyCheckIOS{"SafetyCheckIOS",
                                     base::FEATURE_DISABLED_BY_DEFAULT};
 
 const base::Feature kIllustratedEmptyStates{"IllustratedEmptyStates",
-                                            base::FEATURE_DISABLED_BY_DEFAULT};
+                                            base::FEATURE_ENABLED_BY_DEFAULT};
 
 const base::Feature kSharedHighlightingIOS{"SharedHighlightingIOS",
                                            base::FEATURE_DISABLED_BY_DEFAULT};