NOT YET READY: UMA recording the kind of target frame when extensions pierce browsing instance.

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 e4580c7c456f2a166cbcde31cd93dfa8f4715559..b00820d61711f29309a5dc695d85e6f83fa262ed 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -18636,6 +18636,28 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <summary>Records the container used for a bookmark app launch.</summary>
 </histogram>
 
+<histogram name="Extensions.BrowsingInstanceViolation.ExtensionType"
+    enum="ExtensionType">
+  <owner>lukasza@chromium.org</owner>
+  <summary>
+    When an extension violates browsing instance boundaries, this metric records
+    the extension type of the found frame.
+  </summary>
+</histogram>
+
+<histogram name="Extensions.BrowsingInstanceViolation.ExtensionViewType"
+    enum="ExtensionViewType">
+  <owner>lukasza@chromium.org</owner>
+  <summary>
+    When an extension violates browsing instance boundaries, this metric records
+    the extension view type of the found frame.
+
+    This metric should help confirm or deny the theory that violating browsing
+    instance boundaries is only needed for looking up background contents /
+    pages (of VIEW_TYPE_BACKGROUND_CONTENTS type).
+  </summary>
+</histogram>
+
 <histogram name="Extensions.CheckForExternalUpdatesTime" units="ms">
   <owner>rkaplow@chromium.org</owner>
   <summary>