[omnibox] Disable the instant extended limit on iOS.

This is in preparation for launch. Metrics report:
https://docs.google.com/document/d/1QmvnzeFeFOHx4Bk0MwQCJ261sYSqgrrFFUQUQB4ecUI/edit

Bug: 964049
Change-Id: I5c97ca2dd4c5f00a9340c64261e33fd8213d6b6b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2391644Reviewed-by: Stepan Khapugin <stkhapugin@chromium.org>
Reviewed-by: Mark Pearson <mpearson@chromium.org>
Commit-Queue: Justin Donnelly <jdonnelly@chromium.org>
Cr-Commit-Position: refs/heads/master@{#804363}

components/omnibox/common/omnibox_features.cc

@@ -43,6 +43,13 @@ const auto enabled_by_default_desktop_ios =
     base::FEATURE_ENABLED_BY_DEFAULT;
 #endif
 
+const auto enabled_by_default_android_ios =
+#if defined(OS_ANDROID) || defined(OS_IOS)
+    base::FEATURE_ENABLED_BY_DEFAULT;
+#else
+    base::FEATURE_DISABLED_BY_DEFAULT;
+#endif
+
 // Allows Omnibox to dynamically adjust number of offered suggestions to fill in
 // the space between Omnibox an the soft keyboard. The number of suggestions
 // shown will be no less than minimum for the platform (eg. 5 for Android).
@@ -127,7 +134,7 @@ const base::Feature kAutocompleteTitles{"OmniboxAutocompleteTitles",
 // Returns whether IsInstantExtendedAPIEnabled should be ignored when deciding
 // the number of Google-provided search suggestions.
 const base::Feature kOmniboxDisableInstantExtendedLimit{
-    "OmniboxDisableInstantExtendedLimit", enabled_by_default_android_only};
+    "OmniboxDisableInstantExtendedLimit", enabled_by_default_android_ios};
 
 // Show the search engine logo in the omnibox on Android (desktop already does
 // this).

testing/variations/fieldtrial_testing_config.json

@@ -4616,7 +4616,6 @@
                         "ZeroSuggestVariant:8:*": "RemoteNoUrl"
                     },
                     "enable_features": [
-                        "OmniboxDisableInstantExtendedLimit",
                         "OmniboxOnFocusSuggestions"
                     ]
                 }