Generate trace header/footer in tracing consumer instead of service

services/tracing/trace_data_sink.cc

Index: services/tracing/trace_data_sink.cc
diff --git a/services/tracing/trace_data_sink.cc b/services/tracing/trace_data_sink.cc
index 1abf43ce0f1b69a8424e6c20dd2f3c14f00dbcc2..d1fe93622a8b3a3d48c0b3b3854274d6cde33730 100644
--- a/services/tracing/trace_data_sink.cc
+++ b/services/tracing/trace_data_sink.cc
@@ -10,21 +10,14 @@
 using mojo::common::BlockingCopyFromString;
 
 namespace tracing {
-namespace {
-
-const char kStart[] = "{\"traceEvents\":[";
-const char kEnd[] = "]}";
-
-}  // namespace
 
 TraceDataSink::TraceDataSink(mojo::ScopedDataPipeProducerHandle pipe)
     : pipe_(pipe.Pass()), empty_(true) {
-  BlockingCopyFromString(kStart, pipe_);
 }
 
 TraceDataSink::~TraceDataSink() {
   if (pipe_.is_valid())
-    Flush();
+    pipe_.reset();
   DCHECK(!pipe_.is_valid());
 }
 
@@ -35,9 +28,4 @@ void TraceDataSink::AddChunk(const std::string& json) {
   BlockingCopyFromString(json, pipe_);
 }
 
-void TraceDataSink::Flush() {
-  BlockingCopyFromString(kEnd, pipe_);
-  pipe_.reset();
-}
-
 }  // namespace tracing