Reporting: Implement serializer.

net/reporting/reporting_garbage_collector.h

Index: net/reporting/reporting_garbage_collector.h
diff --git a/net/reporting/reporting_garbage_collector.h b/net/reporting/reporting_garbage_collector.h
index 51b2c70417ba3df7869bfaa96582145ab3fd5b54..17bd9ab56268159caa75c671bb0e456c69de69f8 100644
--- a/net/reporting/reporting_garbage_collector.h
+++ b/net/reporting/reporting_garbage_collector.h
@@ -21,11 +21,19 @@ class ReportingContext;
 // included in too many failed delivery attempts.
 class NET_EXPORT ReportingGarbageCollector {
  public:
+  // Creates a ReportingGarbageCollector. |context| must outlive the garbage
+  // collector.
   static std::unique_ptr<ReportingGarbageCollector> Create(
       ReportingContext* context);
 
   virtual ~ReportingGarbageCollector();
 
+  // Initializes the GarbageCollector, which performs an initial garbage
+  // collection pass over any data already in the Cache.
+  virtual void Initialize() = 0;
+
+  // Replaces the internal Timer used for scheduling garbage collection passes
+  // with a caller-specified one so that unittests can provide a MockTimer.
   virtual void SetTimerForTesting(std::unique_ptr<base::Timer> timer) = 0;
 };