[tracing] Use trace thread for gpu process to initialize tracing

For non-zygote child gpu thread, start the trace thread in
ContentMainRunnerImpl() directly.

For zygote child gpu thread, start the trace thread in RunZygote after
zygote fork and featurelist init.

For Linux & ChromeOS, stop and restart the trace thread when entering
sandbox. Restarting trace thread has a caveat that delayed tasks would
will be lost unless we save them.

This is [3/?] CL of enabling tracing prior to sandboxing.

Bug: 380411640
Change-Id: I89fa94f63a709de0e3da4f8759098c9fff813bee
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6180639
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Reviewed-by: Etienne Pierre-Doray <etiennep@chromium.org>
Commit-Queue: Kramer Ge <fangzhoug@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1428704}

services/tracing/public/cpp/trace_startup.cc

@@ -47,17 +47,15 @@ using base::trace_event::TraceLog;
 }  // namespace
 
 bool g_tracing_initialized_after_featurelist = false;
+bool g_tracing_with_thread = false;
 
 bool IsTracingInitialized() {
   return g_tracing_initialized_after_featurelist;
 }
 
-void EnableStartupTracingIfNeeded() {
+void EnableStartupTracingIfNeeded(bool with_thread) {
   RegisterTracedValueProtoWriter();
 
-  // Create the PerfettoTracedProcess.
-  PerfettoTracedProcess::MaybeCreateInstance();
-
   // Initialize the client library's TrackRegistry to support trace points
   // during startup tracing. We don't setup the client library completely here
   // yet, because we don't have field trials loaded yet (which influence which
@@ -66,6 +64,14 @@ void EnableStartupTracingIfNeeded() {
   // setting up the client library?
   perfetto::internal::TrackRegistry::InitializeInstance();
 
+  // Create the PerfettoTracedProcess.
+  if (with_thread) {
+    g_tracing_with_thread = true;
+    PerfettoTracedProcess::MaybeCreateInstanceWithThread();
+  } else {
+    PerfettoTracedProcess::MaybeCreateInstance();
+  }
+
   // Ensure TraceLog is initialized first.
   // https://crbug.com/764357
   TraceLog::GetInstance();
@@ -106,7 +112,9 @@ void InitTracingPostFeatureList(bool enable_consumer) {
   DCHECK(base::FeatureList::GetInstance());
 
   // Create the PerfettoTracedProcess.
-  PerfettoTracedProcess::MaybeCreateInstance();
+  if (!g_tracing_with_thread) {
+    PerfettoTracedProcess::MaybeCreateInstance();
+  }
   PerfettoTracedProcess::Get().OnThreadPoolAvailable(enable_consumer);
 #if BUILDFLAG(IS_WIN)
   tracing::EnableETWExport();

services/tracing/public/cpp/trace_startup.h

@@ -35,7 +35,8 @@ bool COMPONENT_EXPORT(TRACING_CPP) IsTracingInitialized();
 // TODO(eseckler): Consider allocating the SMB in parent processes outside the
 // sandbox and supply it via the command line. Then, we can revert to call this
 // earlier and from fewer places again.
-void COMPONENT_EXPORT(TRACING_CPP) EnableStartupTracingIfNeeded();
+void COMPONENT_EXPORT(TRACING_CPP)
+    EnableStartupTracingIfNeeded(bool with_thread = false);
 
 // Enable startup tracing for the current process with the provided config. Sets
 // up ProducerClient and trace event and/or sampler profiler data sources, and