perfetto: Emit trace config in TraceEventMetadataSource

If tracing via the new perfetto Consumer API, TracingController won't
emit metadata. Emit the config in the TraceEventMetadataSource instead.

Bug: 950293, 950620
Change-Id: I535e6884e18a167d68788c46827b7bde43a24f8a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1559170
Commit-Queue: Eric Seckler <eseckler@chromium.org>
Auto-Submit: Eric Seckler <eseckler@chromium.org>
Reviewed-by: Sami Kyöstilä <skyostil@chromium.org>
Cr-Commit-Position: refs/heads/master@{#648988}

content/browser/tracing/tracing_controller_impl.cc

@@ -40,6 +40,7 @@
 #include "services/service_manager/public/cpp/connector.h"
 #include "services/tracing/public/cpp/trace_event_agent.h"
 #include "services/tracing/public/cpp/traced_process_impl.h"
+#include "services/tracing/public/cpp/tracing_features.h"
 #include "services/tracing/public/mojom/constants.mojom.h"
 #include "v8/include/v8-version-string.h"
 
@@ -220,7 +221,7 @@ TracingControllerImpl::GenerateMetadataDict() const {
   // this does not happen; however, if the service manager is teared down during
   // tracing, e.g. at Chrome shutdown, tracing controller may finish flushing
   // traces without waiting for tracing agents.
-  if (trace_config_) {
+  if (trace_config_ && !tracing::TracingUsesPerfettoBackend()) {
     DCHECK(IsTracing());
     metadata_dict->SetString("trace-config", trace_config_->ToString());
   }

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

@@ -76,6 +76,9 @@ perfetto::TraceConfig GetDefaultPerfettoConfig(
       perfetto_config.add_data_sources()->mutable_config();
   trace_metadata_config->set_name(tracing::mojom::kMetaDataSourceName);
   trace_metadata_config->set_target_buffer(0);
+  auto* metadata_chrome_config = trace_metadata_config->mutable_chrome_config();
+  metadata_chrome_config->set_trace_config(chrome_config_string);
+  // TODO(ssid): Also set privacy_filtering_enabled here.
 
   return perfetto_config;
 }

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

@@ -23,6 +23,7 @@
 #include "services/tracing/public/cpp/perfetto/thread_local_event_sink.h"
 #include "services/tracing/public/cpp/perfetto/traced_value_proto_writer.h"
 #include "services/tracing/public/cpp/perfetto/track_event_thread_local_event_sink.h"
+#include "services/tracing/public/cpp/trace_event_args_whitelist.h"
 #include "services/tracing/public/mojom/constants.mojom.h"
 #include "third_party/perfetto/include/perfetto/tracing/core/shared_memory_arbiter.h"
 #include "third_party/perfetto/include/perfetto/tracing/core/startup_trace_writer.h"
@@ -42,7 +43,11 @@ using ChromeEventBundleHandle =
 
 TraceEventMetadataSource::TraceEventMetadataSource()
     : DataSourceBase(mojom::kMetaDataSourceName),
-      origin_task_runner_(base::SequencedTaskRunnerHandle::Get()) {}
+      origin_task_runner_(base::SequencedTaskRunnerHandle::Get()) {
+  AddGeneratorFunction(base::BindRepeating(
+      &TraceEventMetadataSource::GenerateTraceConfigMetadataDict,
+      base::Unretained(this)));
+}
 
 TraceEventMetadataSource::~TraceEventMetadataSource() = default;
 
@@ -52,6 +57,30 @@ void TraceEventMetadataSource::AddGeneratorFunction(
   generator_functions_.push_back(generator);
 }
 
+std::unique_ptr<base::DictionaryValue>
+TraceEventMetadataSource::GenerateTraceConfigMetadataDict() {
+  if (chrome_config_.empty()) {
+    return nullptr;
+  }
+
+  base::trace_event::TraceConfig parsed_chrome_config(chrome_config_);
+
+  auto metadata_dict = std::make_unique<base::DictionaryValue>();
+  // If argument filtering is enabled, we need to check if the trace config is
+  // whitelisted before emitting it.
+  // TODO(eseckler): Figure out a way to solve this without calling directly
+  // into IsMetadataWhitelisted().
+  if (!parsed_chrome_config.IsArgumentFilterEnabled() ||
+      IsMetadataWhitelisted("trace-config")) {
+    metadata_dict->SetString("trace-config", chrome_config_);
+  } else {
+    metadata_dict->SetString("trace-config", "__stripped__");
+  }
+
+  chrome_config_ = std::string();
+  return metadata_dict;
+}
+
 void TraceEventMetadataSource::GenerateMetadata(
     std::unique_ptr<perfetto::TraceWriter> trace_writer) {
   DCHECK(origin_task_runner_->RunsTasksInCurrentSequence());
@@ -91,6 +120,7 @@ void TraceEventMetadataSource::StartTracing(
   // sense to emit the metadata on startup, so the UI can display it right away.
   privacy_filtering_enabled_ =
       data_source_config.chrome_config().privacy_filtering_enabled();
+  chrome_config_ = data_source_config.chrome_config().trace_config();
   trace_writer_ =
       producer_client->CreateTraceWriter(data_source_config.target_buffer());
 }
@@ -107,6 +137,7 @@ void TraceEventMetadataSource::StopTracing(
         std::move(stop_complete_callback));
   } else {
     trace_writer_.reset();
+    chrome_config_ = std::string();
     std::move(stop_complete_callback).Run();
   }
 }

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

@@ -51,11 +51,13 @@ class COMPONENT_EXPORT(TRACING_CPP) TraceEventMetadataSource
 
  private:
   void GenerateMetadata(std::unique_ptr<perfetto::TraceWriter> trace_writer);
+  std::unique_ptr<base::DictionaryValue> GenerateTraceConfigMetadataDict();
 
   std::vector<MetadataGeneratorFunction> generator_functions_;
   scoped_refptr<base::SequencedTaskRunner> origin_task_runner_;
   std::unique_ptr<perfetto::TraceWriter> trace_writer_;
   bool privacy_filtering_enabled_ = false;
+  std::string chrome_config_;
 
   DISALLOW_COPY_AND_ASSIGN(TraceEventMetadataSource);
 };