(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 196d3630f3a27df6cd6f09423cda3f9da7d17dbd..f26235801799a76d6b364b542f3ed2af700808d9 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -58525,6 +58525,15 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Security.XFrameOptions" enum="XFrameOptions">
+  <owner>mkwst@chromium.org</owner>
+  <owner>arthursonzogni@chromium.org</owner>
+  <summary>
+    Record uses of the X-Frame-Options header when a page is loaded as an
+    iframe.
+  </summary>
+</histogram>
+
 <histogram name="SequencedWorkerPool.ShutdownDelayTime" units="ms">
   <owner>gab@chromium.org</owner>
   <summary>
@@ -107786,6 +107795,36 @@ value.
   <int value="45" label="Cast"/>
 </enum>
 
+<enum name="XFrameOptions" type="int">
+  <int value="0" label="NONE">
+    A frame is loaded without any X-Frame-Options header.
+  </int>
+  <int value="1" label="DENY">X-Frame-Options: DENY.</int>
+  <int value="2" label="SAMEORIGIN">
+    X-Frame-Options: SAMEORIGIN. The navigation proceeds and every ancestor has
+    the same origin.
+  </int>
+  <int value="3" label="SAMEORIGIN_BLOCKED">
+    X-Frame-Options: SAMEORIGIN. The navigation is blocked because the top-frame
+    doesn't have the same origin.
+  </int>
+  <int value="4" label="SAMEORIGIN_WITH_BAD_ANCESTOR_CHAIN">
+    X-Frame-Options: SAMEORIGIN. The navigation proceeds despite the fact that
+    there is an ancestor that doesn't have the same origin.
+  </int>
+  <int value="5" label="ALLOWALL">X-Frame-Options: ALLOWALL.</int>
+  <int value="6" label="INVALID">
+    Invalid &quot;X-Frame-Options&quot; directive encountered.
+  </int>
+  <int value="7" label="CONFLICT">
+    The frame sets multiple &quot;X-Frame-Options&quot; header with conflicting
+    values.
+  </int>
+  <int value="8" label="BYPASS">
+    The &quot;frame-ancestors&quot; CSP directive should take effect instead.
+  </int>
+</enum>
+
 <enum name="XMLHttpRequestHeaderValueCategoryInRFC7230" type="int">
   <int value="0" label="Header Value Invalid"/>
   <int value="1" label="Header Value Affected By Normalization"/>