Add feature flag for alerts

This is for a new feature where we display price alerts in the Tab card
in the Tab grid switcher as price drops are identified for shopping
related websites.

Bug: 1151401
Change-Id: Id2adfed52195da36ced7ca6baf37a70ac536f686
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2552624Reviewed-by: Theresa  <twellington@chromium.org>
Commit-Queue: David Maunder <davidjm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#830681}

chrome/browser/about_flags.cc

@@ -1697,6 +1697,9 @@ const FeatureEntry::FeatureParam kTabGridLayoutAndroid_TallNTV[] = {
 const FeatureEntry::FeatureParam kTabGridLayoutAndroid_SearchChip[] = {
     {"enable_search_term_chip", "true"}};
 
+const FeatureEntry::FeatureParam kTabGridLayoutAndroid_PriceAlerts[] = {
+    {"enable_price_tracking", "true"}};
+
 const FeatureEntry::FeatureVariation kTabGridLayoutAndroidVariations[] = {
     {"New Tab Variation", kTabGridLayoutAndroid_NewTabVariation,
      base::size(kTabGridLayoutAndroid_NewTabVariation), nullptr},
@@ -1706,6 +1709,8 @@ const FeatureEntry::FeatureVariation kTabGridLayoutAndroidVariations[] = {
      base::size(kTabGridLayoutAndroid_TallNTV), nullptr},
     {"Search term chip", kTabGridLayoutAndroid_SearchChip,
      base::size(kTabGridLayoutAndroid_SearchChip), nullptr},
+    {"Price alerts", kTabGridLayoutAndroid_PriceAlerts,
+     base::size(kTabGridLayoutAndroid_PriceAlerts), nullptr},
 };
 
 const FeatureEntry::FeatureParam kStartSurfaceAndroid_SingleSurface[] = {