Reporting: Implement serializer.

net/reporting/reporting_service.cc

Index: net/reporting/reporting_service.cc
diff --git a/net/reporting/reporting_service.cc b/net/reporting/reporting_service.cc
index 128c510b34f8a2e54869ae1cbc4d6d02c5f7233d..6d2b215ce5f1f2c30b43e3a89d92d780ea445011 100644
--- a/net/reporting/reporting_service.cc
+++ b/net/reporting/reporting_service.cc
@@ -25,7 +25,11 @@ namespace {
 class ReportingServiceImpl : public ReportingService {
  public:
   ReportingServiceImpl(std::unique_ptr<ReportingContext> context)
-      : context_(std::move(context)) {}
+      : context_(std::move(context)) {
+    // TODO(juliatuttle): This can be slow, so it might be better to expose it
+    // as a separate method and call it separately from constructing everything.
+    context_->Initialize();
+  }
 
   ~ReportingServiceImpl() override {}
 
@@ -33,12 +37,14 @@ class ReportingServiceImpl : public ReportingService {
                    const std::string& group,
                    const std::string& type,
                    std::unique_ptr<const base::Value> body) override {
+    DCHECK(context_->initialized());
     context_->cache()->AddReport(url, group, type, std::move(body),
                                  context_->tick_clock()->NowTicks(), 0);
   }
 
   void ProcessHeader(const GURL& url,
                      const std::string& header_value) override {
+    DCHECK(context_->initialized());
     ReportingHeaderParser::ParseHeader(context_.get(), url, header_value);
   }