Adds an option to enable zps on the extension NTP from chrome://flags

Adds an option to chrome://flags/#omnibox-on-focus-suggestions to enable
zero-prefix suggestions on the extension NTP.

Bug: 1035711
Change-Id: I5e327828d9b0d7c2895262b00d221f49af0b256a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1978043
Commit-Queue: Moe Ahmadi <mahmadi@chromium.org>
Reviewed-by: Tommy Li <tommycli@chromium.org>
Cr-Commit-Position: refs/heads/master@{#727015}

chrome/browser/about_flags.cc

@@ -859,10 +859,14 @@ const FeatureEntry::FeatureParam
 const FeatureEntry::FeatureParam
     kOmniboxOnFocusSuggestionsParamNTPRealboxRemoteLocal[] = {
         {"ZeroSuggestVariant:15:*", "RemoteNoUrl,Local"}};
+const FeatureEntry::FeatureParam
+    kOmniboxOnFocusSuggestionsParamExtensionNTPOmniboxRemoteLocal[] = {
+        {"ZeroSuggestVariant:1:*", "RemoteNoUrl,Local"}};
 const FeatureEntry::FeatureParam
     kOmniboxOnFocusSuggestionsParamNTPOmniboxRealboxRemoteLocal[] = {
         *kOmniboxOnFocusSuggestionsParamNTPOmniboxRemoteLocal,
-        *kOmniboxOnFocusSuggestionsParamNTPRealboxRemoteLocal};
+        *kOmniboxOnFocusSuggestionsParamNTPRealboxRemoteLocal,
+        *kOmniboxOnFocusSuggestionsParamExtensionNTPOmniboxRemoteLocal};
 #endif  // defined(OS_ANDROID)
 
 const FeatureEntry::FeatureVariation kOmniboxOnFocusSuggestionsVariations[] = {
@@ -883,7 +887,11 @@ const FeatureEntry::FeatureVariation kOmniboxOnFocusSuggestionsVariations[] = {
      kOmniboxOnFocusSuggestionsParamNTPRealboxRemoteLocal,
      base::size(kOmniboxOnFocusSuggestionsParamNTPRealboxRemoteLocal),
      "t3316133" /* variation_id */},
-    {"NTP Omnibox,Realbox - Remote,Local",
+    {"Extension NTP Omnibox - Remote,Local",
+     kOmniboxOnFocusSuggestionsParamExtensionNTPOmniboxRemoteLocal,
+     base::size(kOmniboxOnFocusSuggestionsParamExtensionNTPOmniboxRemoteLocal),
+     "t3316133" /* variation_id */},
+    {"Everywhere - Remote,Local",
      kOmniboxOnFocusSuggestionsParamNTPOmniboxRealboxRemoteLocal,
      base::size(kOmniboxOnFocusSuggestionsParamNTPOmniboxRealboxRemoteLocal),
      "t3316133" /* variation_id */},