Initial skeleton of custom layouts for Web Notifications.

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 132ec4ad6ecfc4e6222a0494a013c5fcbb2f5573..5641b6f0fe0d66c904ed8fdcffef197600934e44 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -63884,6 +63884,7 @@ To add a new entry, add it with any value and run test to compute valid value.
   <int value="-1184904651" label="enable-npapi"/>
   <int value="-1177802205" label="enable-hosted-app-quit-notification"/>
   <int value="-1172204005" label="enable-offline-auto-reload-visible-only"/>
+  <int value="-1160026273" label="enable-web-notification-custom-layouts"/>
   <int value="-1159563774" label="enable-accessibility-script-injection"/>
   <int value="-1137442543" label="enable-slimming-paint"/>
   <int value="-1136627751" label="ignore-autocomplete-off-autofill"/>
@@ -63891,6 +63892,7 @@ To add a new entry, add it with any value and run test to compute valid value.
   <int value="-1125133283" label="disable-threaded-scrolling"/>
   <int value="-1107762575" label="enable-data-reduction-proxy-config-client"/>
   <int value="-1102212525" label="enable-tcp-fastopen"/>
+  <int value="-1084055006" label="disable-web-notification-custom-layouts"/>
   <int value="-1078093206" label="ash-debug-shortcuts"/>
   <int value="-1077752943" label="enable-password-generation"/>
   <int value="-1062119671" label="enable-password-force-saving"/>