mandoline: write this after lunch.

mojo/services/tracing/public/cpp/tracing_impl.cc

Index: mojo/services/tracing/public/cpp/tracing_impl.cc
diff --git a/mojo/services/tracing/public/cpp/tracing_impl.cc b/mojo/services/tracing/public/cpp/tracing_impl.cc
index 788cd313ccd5fd872f964e32ef3975db11b84ab8..1cffe036d16ced3362bb767e527b71410ff80148 100644
--- a/mojo/services/tracing/public/cpp/tracing_impl.cc
+++ b/mojo/services/tracing/public/cpp/tracing_impl.cc
@@ -4,6 +4,9 @@
 
 #include "mojo/services/tracing/public/cpp/tracing_impl.h"
 
+#include "base/lazy_instance.h"
+#include "base/synchronization/lock.h"
+#include "base/threading/platform_thread.h"
 #include "base/trace_event/trace_event_impl.h"
 #include "mojo/application/public/cpp/application_impl.h"
 
@@ -13,6 +16,22 @@
 #endif
 
 namespace mojo {
+namespace {
+
+// Controls access to |g_tracing_singleton_created|, which can be accessed from
+// different threads.
+base::LazyInstance<base::Lock>::Leaky g_singleton_lock =
+    LAZY_INSTANCE_INITIALIZER;
+
+// Whether we are the first TracingImpl to be created in this mojo
+// application. The first TracingImpl in a physical mojo application connects
+// to the mojo:tracing service.
+//
+// If this is a ContentHandler, it will outlive all its served Applications. If
+// this is a raw mojo application, it is the only Application served.
+bool g_tracing_singleton_created = false;
+
+}
 
 TracingImpl::TracingImpl() {
 }
@@ -21,6 +40,17 @@ TracingImpl::~TracingImpl() {
 }
 
 void TracingImpl::Initialize(ApplicationImpl* app) {
+  {
+    base::AutoLock lock(g_singleton_lock.Get());
+    if (g_tracing_singleton_created)
+      return;
+    g_tracing_singleton_created = true;
+  }
+
+  // This will only set the name for the first app in a loaded mojo file. It's
+  // up to something like CoreServices to name its own child threads.
+  base::PlatformThread::SetName(app->url());
+
   mojo::URLRequestPtr request(mojo::URLRequest::New());
   request->url = mojo::String::From("mojo:tracing");
   connection_ = app->ConnectToApplication(request.Pass());