Add histograms to learn about metrics files dropped for lack of an embedded profile.

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 b99d769b2489f47fde23e8c21ec037eeb70fbae8..e9fa73fc0482a8271de679f2c76d80f728905df8 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -79331,6 +79331,25 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="UMA.FileMetricsProvider.EmbeddedProfile.DroppedFileAge"
+    units="ms">
+  <owner>asvitkine@chromium.org</owner>
+  <owner>bcwhite@chromium.org</owner>
+  <summary>
+    Records the last-modified age of a file that was dropped for lack of an
+    embedded profile.
+  </summary>
+</histogram>
+
+<histogram name="UMA.FileMetricsProvider.EmbeddedProfile.DroppedHistogramCount">
+  <owner>asvitkine@chromium.org</owner>
+  <owner>bcwhite@chromium.org</owner>
+  <summary>
+    Records the number of histograms present in a file that was dropped for lack
+    of an embedded profile.
+  </summary>
+</histogram>
+
 <histogram name="UMA.FileMetricsProvider.EmbeddedProfileResult"
     enum="FileMetricsProviderEmbeddedProfileResult">
   <owner>asvitkine@chromium.org</owner>