Small: Add store specific histograms also.

components/safe_browsing_db/v4_store.cc

Index: components/safe_browsing_db/v4_store.cc
diff --git a/components/safe_browsing_db/v4_store.cc b/components/safe_browsing_db/v4_store.cc
index faf61ec704b09f787eaa40db1bac349d8822406b..8f85ab48dc825032dc36b8efacf0c6baf7551217 100644
--- a/components/safe_browsing_db/v4_store.cc
+++ b/components/safe_browsing_db/v4_store.cc
@@ -33,11 +33,15 @@ const char kApplyUpdate[] = ".ApplyUpdate";
 const char kDecodeAdditions[] = ".DecodeAdditions";
 const char kDecodeRemovals[] = ".DecodeRemovals";
 const char kMergeUpdate[] = ".MergeUpdate";
-// Part 3: Represent the unit of value being measured and logged.
+// Part 3 (optional): Represent the name of the list for which the metric is
+// being logged. For instance, ".UrlSoceng".
+// Part 4: Represent the unit of value being measured and logged.
 const char kResult[] = ".Result";
 const char kTime[] = ".Time";
 // UMA metric names for this file are generated by appending one value each,
-// in order, from parts 1, 2, and 3.
+// in order, from parts [1, 2, and 4], or [1, 2, 3, and 4]. For example:
+// SafeBrowsing.V4ProcessPartialUpdate.ApplyUpdate.Result, or
+// SafeBrowsing.V4ProcessPartialUpdate.ApplyUpdate.UrlSoceng.Result
 
 const uint32_t kFileMagic = 0x600D71FE;
 const uint32_t kFileVersion = 9;