Add favicon database histograms to UMA.

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 889542a37b9d4866abeb04d09386bef4ad79ba84..223486532ae5f312809a1103662201417133905d 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -11277,6 +11277,23 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="History.FaviconDatabaseAdvancedMetricsTime" units="ticks">

[Roger McFarlane (Chromium), 2015/03/25 18:20:19]

To my understanding, ticks doesn't seem like a particular portable unit across
samples? This should really be ms, or similar? The same for
History.DatabaseAdvancedMetricsTime (which this metric copies)?

+  <owner>rogerm@google.com</owner>
+  <summary>
+    The wallclock time taken to gather favicon database metrics.
+  </summary>
+</histogram>
+
+<histogram name="History.FaviconDatabaseSizeMB" units="MB">

[Roger McFarlane (Chromium), 2015/03/25 18:20:19]

I did this in MB to be consistent with the History.DatabaseSizeMB metric;
however, looking at the actual histograms, perhaps both should be in KB instead?

+  <owner>rogerm@google.com</owner>
+  <summary>
+    Size of the Favicons database in MB. This is calculated as the number of
+    pages consumed by the database multiplied by the page size (floored to the
+    next losest MB). So, it does not quite represent the amount of actual data
+    that is in the database.
+  </summary>
+</histogram>
+
 <histogram name="History.FaviconsRecoveredPercentage" units="%">
   <owner>rpop@google.com</owner>
   <summary>
@@ -11314,6 +11331,48 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="History.NumFaviconBitmapsInDB">

[Roger McFarlane (Chromium), 2015/03/25 18:20:19]

This is a pre-existing metric which wasn't declared in histograms.xml

+  <owner>rogerm@google.com</owner>
+  <summary>
+    The total number of favicon bitmaps (of all sizes) cached in a user's
+    Favicon database. A given favicon file/URL may contain multiple bitmap
+    assets at different resolutions/sizes.
+  </summary>
+</histogram>
+
+<histogram name="History.NumFaviconsInDB">
+  <owner>rogerm@google.com</owner>
+  <summary>
+    The total number of favicon files (by favicon URL) being tracked in a user's
+    Favicon database. Note that this metric tracks knowledge of an favicon URL,
+    not whether or not the assets behind that URL are in the favicon cache; see
+    Hisory.NumFaviconBitmapsInDB for that.
+  </summary>
+</histogram>
+
+<histogram name="History.NumLargeFaviconBitmapsInDB">
+  <owner>rogerm@google.com</owner>
+  <summary>
+    The total number of large (i.e., apple touch and similar) favicon bitmaps
+    cached in a user's Favicon database. A given favicon file/URL may contain
+    multiple bitmap assets at different resolutions/sizes. Note that this is a
+    subset of History.NumFaviconBitmapsInDB, which includes all sizes in its
+    count.
+  </summary>
+</histogram>
+
+<histogram name="History.NumLargeFaviconsInDB">
+  <owner>rogerm@google.com</owner>
+  <summary>
+    The total number of large (i.e., apple touch and similar) favicon files
+    being tracked in a user's Favicon database. Note that this is a subset of
+    History.NumFaviconsInDB, which includes all sizes in its count. Further note
+    that this metric tracks knowledge of a large favicon URL, not whether or not
+    the assets behind that URL are in the favicon cache; see
+    History.NumLargeFaviconBitmapsInDB for that.
+  </summary>
+</histogram>
+
 <histogram name="History.TopSitesRecoveredPercentage" units="%">
   <owner>Please list the metric's owners. Add more owner tags as needed.</owner>
   <summary>