Trace-based benchmarking via a mojo app.

mojo/common/tracing_impl.cc

Index: mojo/common/tracing_impl.cc
diff --git a/mojo/common/tracing_impl.cc b/mojo/common/tracing_impl.cc
index 2a6eac1e92fc02c8a4110c1fa31d066cab981296..db158dda8446da92b221b0dc3f519bb83a81c45a 100644
--- a/mojo/common/tracing_impl.cc
+++ b/mojo/common/tracing_impl.cc
@@ -24,7 +24,11 @@ void TracingImpl::Initialize(ApplicationImpl* app) {
 
 void TracingImpl::Create(ApplicationConnection* connection,
                          InterfaceRequest<tracing::TraceProvider> request) {
-  new TraceProviderImpl(request.Pass());
+  TraceProviderImpl* trace_provider_impl =
+      new TraceProviderImpl(request.Pass());
+  if (tracing_already_started_) {
+    trace_provider_impl->set_tracing_already_started(tracing_already_started_);
+  }
 }
 
 }  // namespace mojo