Added histograms descriptions for History DB.

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 d9c2dd62b43f580b82e97832591fe4c50d2336dd..92da55f21ed434221cbfdf0353b873e006edccc0 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -13279,6 +13279,33 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="History.DatabaseAdvancedMetricsTime" units="milliseconds">
+  <owner>shess@chromium.org</owner>
+  <summary>
+    Time spent on advanced History DB metrics calculation (weekly and monthly
+    URL, host, and category counts). Advanced metrics are logged on
+    initialization of the History DB on 0.3% of starts.
+  </summary>
+</histogram>
+
+<histogram name="History.DatabaseBasicMetricsTime" units="milliseconds">
+  <owner>shess@chromium.org</owner>
+  <summary>
+    Time spent on basic History DB metrics calculation (file size and table
+    counts). Basic metrics are logged on initialization of the History DB on 1%
+    of starts.
+  </summary>
+</histogram>
+
+<histogram name="History.DatabaseFileMB" units="MB">
+  <owner>shess@chromium.org</owner>
+  <summary>
+    Size of History DB file. Duplicate of Profile.HistorySize and
+    Sqlite.SizeKB.History. Logged on initialization of the History DB on 1% of
+    starts.
+  </summary>
+</histogram>
+
 <histogram name="History.DeleteFTSIndexDatabases">
   <owner>Please list the metric's owners. Add more owner tags as needed.</owner>
   <summary>
@@ -13368,6 +13395,32 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="History.MonthlyHostCount">
+  <owner>shess@chromium.org</owner>
+  <summary>
+    Unique hostnames in History database urls table with last-visit times in the
+    last 30 days. Metrics are logged on initialization of the History DB on 0.3%
+    of starts.
+  </summary>
+</histogram>
+
+<histogram name="History.MonthlyURLCount">
+  <owner>shess@chromium.org</owner>
+  <summary>
+    Unique URLs in History database urls table with last-visit times in the last
+    30 days. Metrics are logged on initialization of the History DB on 0.3% of
+    starts.
+  </summary>
+</histogram>
+
+<histogram name="History.MonthlyVisitCount">
+  <owner>shess@chromium.org</owner>
+  <summary>
+    Number of rows in History visits table with visit times in the last 30 days.
+    Metrics are logged on initialization of the History DB on 1% of starts.
+  </summary>
+</histogram>
+
 <histogram name="History.NumFaviconBitmapsInDB">
   <owner>rogerm@chromium.org</owner>
   <summary>
@@ -13484,6 +13537,48 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="History.URLTableCount">
+  <owner>shess@chromium.org</owner>
+  <summary>
+    Number of rows in urls table in History DB. Metrics are logged on
+    initialization of the History DB on 1% of starts.
+  </summary>
+</histogram>
+
+<histogram name="History.VisitTableCount">
+  <owner>shess@chromium.org</owner>
+  <summary>
+    Number of rows in visits table in History DB. Metrics are logged on
+    initialization of the History DB on 1% of starts.
+  </summary>
+</histogram>
+
+<histogram name="History.WeeklyHostCount">
+  <owner>shess@chromium.org</owner>
+  <summary>
+    Unique hostnames in History database urls table with last-visit times in the
+    last 7 days. Metrics are logged on initialization of the History DB on 0.3%
+    of starts.
+  </summary>
+</histogram>
+
+<histogram name="History.WeeklyURLCount">
+  <owner>shess@chromium.org</owner>
+  <summary>
+    Unique URLs in History database urls table with last-visit times in the last
+    7 days. Metrics are logged on initialization of the History DB on 0.3% of
+    starts.
+  </summary>
+</histogram>
+
+<histogram name="History.WeeklyVisitCount">
+  <owner>shess@chromium.org</owner>
+  <summary>
+    Number of rows in History visits table with visit times in the last 7 days.
+    Metrics are logged on initialization of the History DB on 1% of starts.
+  </summary>
+</histogram>
+
 <histogram name="HistoryPage.ClickPosition">
   <owner>rpop@google.com</owner>
   <summary>
@@ -42559,6 +42654,13 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <summary>Error codes returned by sqlite for the history db.</summary>
 </histogram>
 
+<histogram name="Sqlite.Migration.History" units="milliseconds">
+  <owner>shess@chromium.org</owner>
+  <summary>
+    Time used to migrate History database schema to a new version.
+  </summary>
+</histogram>
+
 <histogram name="Sqlite.OpenFailure" enum="SqliteErrorCode">
   <owner>shess@chromium.org</owner>
   <summary>Error which prevented database open.</summary>