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 e7e8a1865bd2f6510381b07820480d05b93165f5..05f3d6e558e92624a72958ed8749ff79886169ab 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -8696,6 +8696,15 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="DeferredFrameLoading.StatesV1"
+    enum="FrameStateForDeferredLoading">
+  <owner>dgrogan@chromium.org</owner>
+  <summary>
+    Why and if subframes would be loaded in a world where we defer loading until
+    they are visible or are important for cross-origin communication.
+  </summary>
+</histogram>
+
 <histogram name="DevTools.ActionTaken" enum="DevToolsAction">
   <owner>sergeyv@chromium.org</owner>
   <owner>vsevik@chromium.org</owner>
@@ -80007,6 +80016,11 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <int value="3" label="Allowed navigation, user gesture"/>
 </enum>
 
+<enum name="FrameStateForDeferredLoading" type="int">
+  <int value="0" label="Created"/>
+  <int value="1" label="WouldLoadBecauseVisible"/>
+</enum>
+
 <enum name="FtpDataConnectionError" type="int">
   <int value="0">Data connection successful</int>
   <int value="1">Local firewall blocked the connection</int>