Add Custom Feeback Flag to about://flags

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index 726486723b0b73f6ac304ab80795f1a4b16e5ad5..6ee508df9744e4038ad84502ebfdba4e42a91401 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -98333,6 +98333,7 @@ value.
   <int value="-472013317" label="WebRTC-H264WithOpenH264FFmpeg:disabled"/>
   <int value="-462205750" label="enable-service-worker-sync"/>
   <int value="-461292699" label="ContentSuggestionsCategoryOrder:enabled"/>
+  <int value="-460081932" label="CustomFeedbackUi:disabled"/>
   <int value="-455203267" label="use_new_features_summary"/>
   <int value="-449465495" label="disable-browser-task-scheduler"/>
   <int value="-430360431" label="disable-password-generation"/>
@@ -98562,6 +98563,7 @@ value.
   <int value="584541349" label="ContextualSearchSingleActions:disabled"/>
   <int value="592050831" label="disable-slimming-paint"/>
   <int value="593707592" label="disable-network-portal-notification"/>
+  <int value="596106994" label="CustomFeedbackUi:enabled"/>
   <int value="598827460" label="enable-roboto-font-ui"/>
   <int value="602117675" label="NTPBookmarkSuggestions:enabled"/>
   <int value="603326800" label="UsePasswordSeparatedSigninFlow:enabled"/>