Perfetto: Serialize ConvertableToTraceFormat to a JSON string field

This will act as a fallback while derived types are converted
to their own optimized proto messages.

Dependent on https://android-review.googlesource.com/c/platform/external/perfetto/+/699955
being rolled into third_party/perfetto first.

Bug: 839063
Change-Id: I00fc5a639a770d06fbf08c60fb43d12871aa69c7
Reviewed-on: https://chromium-review.googlesource.com/1087643Reviewed-by: Primiano Tucci <primiano@chromium.org>
Reviewed-by: Sami Kyöstilä <skyostil@chromium.org>
Commit-Queue: oysteine <oysteine@chromium.org>
Cr-Commit-Position: refs/heads/master@{#565080}

base/trace_event/trace_event_impl.h

@@ -146,6 +146,10 @@ class BASE_EXPORT TraceEvent {
   const char* arg_name(size_t index) const { return arg_names_[index]; }
   const TraceValue& arg_value(size_t index) const { return arg_values_[index]; }
 
+  const ConvertableToTraceFormat* arg_convertible_value(size_t index) const {
+    return convertable_values_[index].get();
+  }
+
 #if defined(OS_ANDROID)
   void SendToATrace();
 #endif

services/tracing/perfetto/json_trace_exporter.cc

@@ -162,6 +162,11 @@ void OutputJSONFromTraceEventProto(
       TraceEvent::AppendValueAsJSON(TRACE_VALUE_TYPE_STRING, value, out);
       continue;
     }
+
+    if (arg.has_json_value()) {
+      *out += arg.json_value();
+      continue;
+    }
   }
 
   *out += "}}";

services/tracing/perfetto/json_trace_exporter_unittest.cc

@@ -431,4 +431,35 @@ TEST_F(JSONTraceExporterTest, TestEventWithPointerArgs) {
   EXPECT_EQ("0x2", trace_event->GetKnownArgAsString("foo2"));
 }
 
+TEST_F(JSONTraceExporterTest, TestEventWithConvertableArgs) {
+  CreateJSONTraceExporter("foo");
+  service()->WaitForTracingEnabled();
+  StopAndFlush();
+
+  perfetto::protos::TracePacket trace_packet_proto;
+  auto* new_trace_event =
+      trace_packet_proto.mutable_chrome_events()->add_trace_events();
+  SetTestPacketBasicData(new_trace_event);
+
+  {
+    auto* new_arg = new_trace_event->add_args();
+    new_arg->set_name("foo1");
+    new_arg->set_json_value("\"conv_value1\"");
+  }
+
+  {
+    auto* new_arg = new_trace_event->add_args();
+    new_arg->set_name("foo2");
+    new_arg->set_json_value("\"conv_value2\"");
+  }
+
+  FinalizePacket(trace_packet_proto);
+
+  service()->WaitForTracingDisabled();
+  auto* trace_event = ValidateAndGetBasicTestPacket();
+
+  EXPECT_EQ("conv_value1", trace_event->GetKnownArgAsString("foo1"));
+  EXPECT_EQ("conv_value2", trace_event->GetKnownArgAsString("foo2"));
+}
+
 }  // namespace tracing

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

@@ -90,16 +90,16 @@ class TraceEventDataSource::ThreadLocalEventSink {
     for (int i = 0;
          i < base::trace_event::kTraceMaxNumArgs && trace_event.arg_name(i);
          ++i) {
-      // TODO(oysteine): Support ConvertableToTraceFormat serialized into a JSON
-      // string.
       auto type = trace_event.arg_type(i);
+      auto* new_arg = new_trace_event->add_args();
+      new_arg->set_name(trace_event.arg_name(i));
+
       if (type == TRACE_VALUE_TYPE_CONVERTABLE) {
+        std::string json = trace_event.arg_convertible_value(i)->ToString();
+        new_arg->set_json_value(json.c_str());
         continue;
       }
 
-      auto* new_arg = new_trace_event->add_args();
-      new_arg->set_name(trace_event.arg_name(i));
-
       auto& value = trace_event.arg_value(i);
       switch (type) {
         case TRACE_VALUE_TYPE_BOOL:

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

@@ -339,6 +339,49 @@ TEST_F(TraceEventDataSourceTest, EventWithPointerArgs) {
   EXPECT_EQ(static_cast<uintptr_t>(0xF00D), trace_args[1].pointer_value());
 }
 
+TEST_F(TraceEventDataSourceTest, EventWithConvertableArgs) {
+  static const char kArgValue1[] = "\"conv_value1\"";
+  static const char kArgValue2[] = "\"conv_value2\"";
+
+  CreateTraceEventDataSource();
+
+  int num_calls = 0;
+
+  class Convertable : public base::trace_event::ConvertableToTraceFormat {
+   public:
+    explicit Convertable(int* num_calls, const char* arg_value)
+        : num_calls_(num_calls), arg_value_(arg_value) {}
+    ~Convertable() override = default;
+
+    void AppendAsTraceFormat(std::string* out) const override {
+      (*num_calls_)++;
+      out->append(arg_value_);
+    }
+
+   private:
+    int* num_calls_;
+    const char* arg_value_;
+  };
+
+  std::unique_ptr<Convertable> conv1(new Convertable(&num_calls, kArgValue1));
+  std::unique_ptr<Convertable> conv2(new Convertable(&num_calls, kArgValue2));
+
+  TRACE_EVENT_INSTANT2(kCategoryGroup, "bar", TRACE_EVENT_SCOPE_THREAD,
+                       "foo_arg1", std::move(conv1), "foo_arg2",
+                       std::move(conv2));
+
+  EXPECT_EQ(2, num_calls);
+
+  auto trace_events = producer_client()->GetChromeTraceEvents();
+  EXPECT_EQ(trace_events.size(), 1);
+
+  auto trace_args = trace_events[0].args();
+  EXPECT_EQ(trace_args.size(), 2);
+
+  EXPECT_EQ(kArgValue1, trace_args[0].json_value());
+  EXPECT_EQ(kArgValue2, trace_args[1].json_value());
+}
+
 TEST_F(TraceEventDataSourceTest, CompleteTraceEventsIntoSeparateBeginAndEnd) {
   static const char kEventName[] = "bar";