Log to UMA when x-origin frames (1) are created and (2) become visible

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 ccb015218961048b5dfb1b1cfa73160813bd231d..d26a5a5ca240ad0e289c621ce80bec2f865a244e 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -26209,6 +26209,15 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Navigation.DeferredDocumentLoading.StatesV1"
+    enum="DocumentStateForDeferredLoading">
+  <owner>dgrogan@chromium.org</owner>
+  <summary>
+    Why and if cross-origin documents would be loaded in a world where we defer
+    loading until they are visible.
+  </summary>
+</histogram>
+
 <histogram name="Navigation.EngagementTime.HTTP" units="ms">
   <owner>felt@chromium.org</owner>
   <summary>
@@ -74633,6 +74642,11 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <int value="3" label="Keyboard"/>
 </enum>
 
+<enum name="DocumentStateForDeferredLoading" type="int">
+  <int value="0" label="Created"/>
+  <int value="1" label="WouldLoadBecauseVisible"/>
+</enum>
+
 <enum name="DocumentWriteGatedEvaluation" type="int">
   <int value="0" label="Script too long"/>
   <int value="1" label="No likely external script write"/>