[iOS] Add flag for zero-suggest on NTP

This extends the definition of kZeroSuggestionsOnNTP from
Desktop/Android to iOS.

Bug: 1048193
Change-Id: I593c8dfd287a20b7afb9b4041ce6c33abbb99c22
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2036030
Commit-Queue: Robbie Gibson <rkgibson@google.com>
Reviewed-by: Stepan Khapugin <stkhapugin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#738183}

ios/chrome/browser/flags/about_flags.mm

@@ -467,6 +467,10 @@ const flags_ui::FeatureEntry kFeatureEntries[] = {
      flags_ui::kOsIos,
      FEATURE_VALUE_TYPE(
          omnibox::kOmniboxPreserveDefaultMatchAgainstAsyncUpdate)},
+    {"omnibox-zero-suggestions-on-ntp",
+     flag_descriptions::kOmniboxZeroSuggestionsOnNTPName,
+     flag_descriptions::kOmniboxZeroSuggestionsOnNTPDescription,
+     flags_ui::kOsIos, FEATURE_VALUE_TYPE(omnibox::kZeroSuggestionsOnNTP)},
     {"enable-send-tab-to-self-broadcast",
      flag_descriptions::kSendTabToSelfBroadcastName,
      flag_descriptions::kSendTabToSelfBroadcastDescription, flags_ui::kOsIos,

ios/chrome/browser/flags/ios_chrome_flag_descriptions.cc

@@ -310,6 +310,11 @@ const char kOmniboxOnDeviceHeadSuggestionsDescription[] =
     "Shows Google head non personalized search suggestions provided by a "
     "compact on device model";
 
+const char kOmniboxZeroSuggestionsOnNTPName[] =
+    "Omnibox Zero Suggestions on New Tab Page";
+const char kOmniboxZeroSuggestionsOnNTPDescription[] =
+    "Offer suggestions when URL bar (omnibox) is focused.";
+
 const char kPageInfoRefactoringName[] = "New design of the page info";
 const char kPageInfoRefactoringDescription[] =
     "Uses the new design for the page security info.";

ios/chrome/browser/flags/ios_chrome_flag_descriptions.h

@@ -265,6 +265,11 @@ extern const char kOmniboxUIMaxAutocompleteMatchesDescription[];
 extern const char kOmniboxOnDeviceHeadSuggestionsName[];
 extern const char kOmniboxOnDeviceHeadSuggestionsDescription[];
 
+// Title and description for the flag to enable omnibox zero-state suggestions
+// on the NTP.
+extern const char kOmniboxZeroSuggestionsOnNTPName[];
+extern const char kOmniboxZeroSuggestionsOnNTPDescription[];
+
 // Title and description for the flag to enable the new design of the page info.
 extern const char kPageInfoRefactoringName[];
 extern const char kPageInfoRefactoringDescription[];