[background_tracing] Allow DoEmitNamedTrigger to be called from any

sequence

Bug: 394973090
Change-Id: I956c934e675750ee808a8eb3238711a8afa6b484
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6244400
Commit-Queue: Thiabaud Engelbrecht <thiabaud@google.com>
Reviewed-by: Etienne Pierre-Doray <etiennep@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1417579}

services/tracing/public/cpp/background_tracing/background_tracing_agent_impl.cc

@@ -17,7 +17,8 @@ namespace tracing {
 
 BackgroundTracingAgentImpl::BackgroundTracingAgentImpl(
     mojo::PendingRemote<mojom::BackgroundTracingAgentClient> client)
-    : client_(std::move(client)) {
+    : client_(std::move(client)),
+      task_runner_{base::SequencedTaskRunner::GetCurrentDefault()} {
   client_->OnInitialized();
   NamedTriggerManager::SetInstance(this);
 }
@@ -53,9 +54,22 @@ bool BackgroundTracingAgentImpl::DoEmitNamedTrigger(
     std::optional<int32_t> value) {
   TRACE_EVENT_INSTANT("latency", "NamedTrigger",
                       base::trace_event::TriggerFlow(trigger_name, value));
+  DoEmitNamedTriggerImpl(trigger_name, value);
+  return true;
+}
+
+void BackgroundTracingAgentImpl::DoEmitNamedTriggerImpl(
+    const std::string& trigger_name,
+    std::optional<int32_t> value) {
+  if (!task_runner_->RunsTasksInCurrentSequence()) {
+    task_runner_->PostTask(
+        FROM_HERE,
+        base::BindOnce(&BackgroundTracingAgentImpl::DoEmitNamedTriggerImpl,
+                       weak_factory_.GetWeakPtr(), trigger_name, value));
+    return;
+  }
   client_->OnTriggerBackgroundTrace(
       tracing::mojom::BackgroundTracingRule::New(trigger_name), value);
-  return true;
 }
 
 void BackgroundTracingAgentImpl::OnHistogramChanged(

services/tracing/public/cpp/background_tracing/background_tracing_agent_impl.h

@@ -52,6 +52,9 @@ class COMPONENT_EXPORT(BACKGROUND_TRACING_CPP) BackgroundTracingAgentImpl
                           uint64_t name_hash,
                           base::Histogram::Sample32 actual_value);
 
+  void DoEmitNamedTriggerImpl(const std::string& trigger_name,
+                              std::optional<int32_t> value);
+
   mojo::Remote<mojom::BackgroundTracingAgentClient> client_;
   base::Time histogram_last_changed_;
   // Tracks histogram names and corresponding registered callbacks.
@@ -60,6 +63,7 @@ class COMPONENT_EXPORT(BACKGROUND_TRACING_CPP) BackgroundTracingAgentImpl
       std::unique_ptr<base::StatisticsRecorder::ScopedHistogramSampleObserver>>
       histogram_callback_map_;
 
+  scoped_refptr<base::SequencedTaskRunner> task_runner_;
   base::WeakPtrFactory<BackgroundTracingAgentImpl> weak_factory_{this};
 };