perfetto: Make ProducerClient a singleton

So that we can access the process-wide client from other tracing agents.

Bug: 900603
Change-Id: Ie157ecc6c5e59e449c8e8182d3a2b31ea8b1bd9e
Reviewed-on: https://chromium-review.googlesource.com/c/1335588Reviewed-by: Sami Kyöstilä <skyostil@chromium.org>
Reviewed-by: oysteine <oysteine@chromium.org>
Commit-Queue: Eric Seckler <eseckler@chromium.org>
Cr-Commit-Position: refs/heads/master@{#607995}

services/tracing/public/cpp/perfetto/producer_client.cc

@@ -47,6 +47,12 @@ void ProducerClient::DataSourceBase::StartTracingWithID(
   StartTracing(producer_client, data_source_config);
 }
 
+// static
+ProducerClient* ProducerClient::Get() {
+  static base::NoDestructor<ProducerClient> producer_client;
+  return producer_client.get();
+}
+
 ProducerClient::ProducerClient() : weak_ptr_factory_(this) {
   DETACH_FROM_SEQUENCE(sequence_checker_);
 }

services/tracing/public/cpp/perfetto/producer_client.h

@@ -70,7 +70,9 @@ class COMPONENT_EXPORT(TRACING_CPP) ProducerClient
     std::string name_;
   };
 
-  ProducerClient();
+  // Returns the process-wide instance of the ProducerClient.
+  static ProducerClient* Get();
+
   ~ProducerClient() override;
 
   static void DeleteSoonForTesting(std::unique_ptr<ProducerClient>);
@@ -125,7 +127,13 @@ class COMPONENT_EXPORT(TRACING_CPP) ProducerClient
 
   static void ResetTaskRunnerForTesting();
 
+ protected:
+  // protected for testing.
+  ProducerClient();
+
  private:
+  friend class base::NoDestructor<ProducerClient>;
+
   void CommitDataOnSequence(mojom::CommitDataRequestPtr request);
   void AddDataSourceOnSequence(DataSourceBase*);
   void RegisterDataSourceWithHost(DataSourceBase* data_source);

services/tracing/public/cpp/trace_event_agent.cc

@@ -46,16 +46,12 @@ namespace tracing {
 
 namespace {
 
-ProducerClient* GetProducerClient() {
-  static base::NoDestructor<ProducerClient> producer_client;
-  return producer_client.get();
-}
-
 void InitializeProducerClient(service_manager::Connector* connector) {
   mojom::PerfettoServicePtr perfetto_service;
   connector->BindInterface(mojom::kServiceName, &perfetto_service);
 
-  GetProducerClient()->CreateMojoMessagepipes(base::BindOnce(
+  ProducerClient* client = ProducerClient::Get();
+  client->CreateMojoMessagepipes(base::BindOnce(
       [](mojom::PerfettoServicePtr perfetto_service,
          mojom::ProducerClientPtr producer_client_pipe,
          mojom::ProducerHostRequest producer_host_pipe) {
@@ -64,7 +60,7 @@ void InitializeProducerClient(service_manager::Connector* connector) {
       },
       std::move(perfetto_service)));
 
-  GetProducerClient()->AddDataSource(TraceEventDataSource::GetInstance());
+  client->AddDataSource(TraceEventDataSource::GetInstance());
 }
 
 void AddPerfettoMetadataGeneratorFunction(
@@ -73,7 +69,7 @@ void AddPerfettoMetadataGeneratorFunction(
   // call.
   static TraceEventMetadataSource* metadata_source = []() {
     static base::NoDestructor<TraceEventMetadataSource> instance;
-    GetProducerClient()->AddDataSource(instance.get());
+    ProducerClient::Get()->AddDataSource(instance.get());
     return instance.get();
   }();