Log the size of each of the stores and complete DB on launch and after each

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 6985dada5c972a922c69887a6263e1836bb7eaae..6ec495b3ec5f4d5ab1450f7ea9dd34f8f18a47d4 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -51741,6 +51741,14 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="SafeBrowsing.V4Database.Size" units="KB">
+  <owner>vakh@chromium.org</owner>
+  <summary>
+    The size of the SafeBrowsing database or file on disk in kilobytes, after
+    reading it from disk on startup and after a database update has occurred.
+  </summary>
+</histogram>
+
 <histogram name="SafeBrowsing.V4DecodeAdditionsResult"
     enum="SafeBrowsingV4DecodeResult">
   <obsolete>
@@ -109889,6 +109897,7 @@ value.
 
 <histogram_suffixes name="SafeBrowsing.V4Store.Metrics" separator="."
     ordering="prefix">
+  <affected-histogram name="SafeBrowsing.V4Database.Size"/>
   <suffix name="UrlMalware"/>
   <suffix name="UrlSoceng"/>
   <suffix name="UrlUws"/>