(Re-)introduce AncestorThrottle to handle 'X-Frame-Options'.

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 b89fe2e12b3e93d46614819bb68c4148319e6e5e..c30067a4c6daec6bf045530aaef34f81370ff88c 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -58032,6 +58032,15 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Security.XFrameOptions.SameOrigin"
+    enum="XFrameOptionsSameOrigin">
+  <owner>mkwst@chromium.org</owner>
+  <summary>
+    Record uses of the &quot;SAMEORIGIN&quot; directive for the
+    &quot;X-Frame-Options&quot; header when a page tries to load an iframe.
+  </summary>
+</histogram>
+
 <histogram name="SequencedWorkerPool.ShutdownDelayTime" units="ms">
   <owner>gab@chromium.org</owner>
   <summary>
@@ -106608,6 +106617,13 @@ value.
   <int value="45" label="Cast"/>
 </enum>
 
+<enum name="XFrameOptionsSameOrigin" type="int">
+  <int value="0" label="Total"/>
+  <int value="1" label="SAMEORIGIN"/>
+  <int value="2" label="SAMEORIGIN blocked"/>
+  <int value="3" label="SAMEORIGIN with bad ancestor chain"/>
+</enum>
+
 <enum name="XMLHttpRequestHeaderValueCategoryInRFC7230" type="int">
   <int value="0" label="Header Value Invalid"/>
   <int value="1" label="Header Value Affected By Normalization"/>