Support for tracing app initialization.

mojo/common/trace_provider_impl.cc

Index: mojo/common/trace_provider_impl.cc
diff --git a/mojo/common/trace_provider_impl.cc b/mojo/common/trace_provider_impl.cc
index 8ffc867a46f38192022891ad5fe9adb797c9fb06..4ebb1f0e60627abcbe1bb4619c51cd2ce427b597 100644
--- a/mojo/common/trace_provider_impl.cc
+++ b/mojo/common/trace_provider_impl.cc
@@ -12,19 +12,16 @@
 
 namespace mojo {
 
-TraceProviderImpl::TraceProviderImpl(
-    InterfaceRequest<tracing::TraceProvider> request)
-    : tracing_already_started_(false), binding_(this, request.Pass()) {
-}
+TraceProviderImpl::TraceProviderImpl() : tracing_forced_(false) {}
 
-TraceProviderImpl::~TraceProviderImpl() {
-}
+TraceProviderImpl::~TraceProviderImpl() {}
 
 void TraceProviderImpl::StartTracing(const String& categories,
                                      tracing::TraceRecorderPtr collector) {
   DCHECK(!recorder_.get());
   recorder_ = collector.Pass();
-  if (!tracing_already_started_) {
+  tracing_forced_ = false;
+  if (!base::trace_event::TraceLog::GetInstance()->IsEnabled()) {
     std::string categories_str = categories.To<std::string>();
     base::trace_event::TraceLog::GetInstance()->SetEnabled(
         base::trace_event::TraceConfig(categories_str,
@@ -41,6 +38,37 @@ void TraceProviderImpl::StopTracing() {
       base::Bind(&TraceProviderImpl::SendChunk, base::Unretained(this)));
 }
 
+void TraceProviderImpl::EnableTracingNow() {
+  base::trace_event::TraceLog::GetInstance()->SetEnabled(
+      base::trace_event::TraceConfig("*", base::trace_event::RECORD_UNTIL_FULL),
+      base::trace_event::TraceLog::RECORDING_MODE);
+  tracing_forced_ = true;
+  base::MessageLoop::current()->PostTask(
+      FROM_HERE,
+      base::Bind(&TraceProviderImpl::DelayedStop, base::Unretained(this)));

[qsr, 2015/09/11 14:44:04]

What is the lifecycle of this object. Are you guaranteed it will still be there
when this comes back (or worst after 1 second?)

[etiennej, 2015/09/11 15:07:32]

Fixed.

+}
+
+void TraceProviderImpl::DelayedStop() {
+  // We use this indirection to account for cases where the Initialize app
+  // method (within which TraceProviderImpl is created) takes more than one
+  // second to finish; thus we start the countdown only when the current thread
+  // is unblocked.
+  base::MessageLoop::current()->PostDelayedTask(
+      FROM_HERE,
+      base::Bind(&TraceProviderImpl::StopIfForced, base::Unretained(this)),
+      base::TimeDelta::FromSeconds(1));
+}
+
+void TraceProviderImpl::StopIfForced() {
+  if (!tracing_forced_) {
+    return;
+  }
+  base::trace_event::TraceLog::GetInstance()->SetDisabled();
+  base::trace_event::TraceLog::GetInstance()->Flush(
+      base::Callback<void(const scoped_refptr<base::RefCountedString>&,
+                          bool)>());
+}
+
 void TraceProviderImpl::SendChunk(
     const scoped_refptr<base::RefCountedString>& events_str,
     bool has_more_events) {