bug 1101194 - add telemetry for DataStorage table size r=mgoodwin

security/manager/boot/src/DataStorage.cpp

@@ -8,6 +8,7 @@
 
 #include "mozilla/Preferences.h"
 #include "mozilla/Services.h"
+#include "mozilla/Telemetry.h"
 #include "mozilla/unused.h"
 #include "nsAppDirectoryServiceDefs.h"
 #include "nsDirectoryServiceUtils.h"
@@ -110,6 +111,12 @@ private:
 
 DataStorage::Reader::~Reader()
 {
+  {
+    MutexAutoLock lock(mDataStorage->mMutex);
+    Telemetry::Accumulate(Telemetry::DATA_STORAGE_ENTRIES,
+                          mDataStorage->mPersistentDataTable.Count());
+  }
+
   // Notify that calls to Get can proceed.
   {
     MonitorAutoLock readyLock(mDataStorage->mReadyMonitor);

toolkit/components/telemetry/Histograms.json

@@ -7069,5 +7069,12 @@
     "kind": "count",
     "keyed": true,
     "description": "Counts of plugin and content process crashes which are reported with a crash dump."
+  },
+  "DATA_STORAGE_ENTRIES": {
+    "expires_in_version": "default",
+    "kind": "linear",
+    "high": "1024",
+    "n_buckets": 16,
+    "description": "The number of entries in persistent DataStorage (HSTS and HPKP data, basically)"
   }
 }