Internalize JSON chunk management to trace_event.h API.

base/debug/trace_event.cc

Index: base/debug/trace_event.cc
diff --git a/base/debug/trace_event.cc b/base/debug/trace_event.cc
index 347644f982ef3a4f3cd260b55a8b452e5217db3e..3e03d4afae69a0a909658a40f1b0ea70bf97c015 100644
--- a/base/debug/trace_event.cc
+++ b/base/debug/trace_event.cc
@@ -9,6 +9,7 @@
 #if defined(OS_WIN)
 #include "base/debug/trace_event_win.h"
 #endif
+#include "base/bind.h"
 #include "base/format_macros.h"
 #include "base/memory/ref_counted_memory.h"
 #include "base/process_util.h"
@@ -224,13 +225,11 @@ void TraceEvent::AppendEventsAsJSON(const std::vector<TraceEvent>& events,
                                     size_t start,
                                     size_t count,
                                     std::string* out) {
-  *out += "[";
   for (size_t i = 0; i < count && start + i < events.size(); ++i) {
     if (i > 0)
       *out += ",";
     events[i + start].AppendAsJSON(out);
   }
-  *out += "]";
 }
 
 void TraceEvent::AppendAsJSON(std::string* out) const {
@@ -262,6 +261,48 @@ void TraceEvent::AppendAsJSON(std::string* out) const {
 
 ////////////////////////////////////////////////////////////////////////////////
 //
+// TraceResultBuffer
+//
+////////////////////////////////////////////////////////////////////////////////
+
+TraceResultBuffer::OutputCallback
+    TraceResultBuffer::SimpleOutput::GetCallback() {
+  return base::Bind(&SimpleOutput::Append, base::Unretained(this));
+}
+
+void TraceResultBuffer::SimpleOutput::Append(
+    const std::string& json_trace_output) {
+  json_output += json_trace_output;
+}
+
+TraceResultBuffer::TraceResultBuffer() : append_comma_(false) {
+}
+
+TraceResultBuffer::~TraceResultBuffer() {
+}
+
+void TraceResultBuffer::SetOutputCallback(OutputCallback json_chunk_callback) {
+  output_callback_ = json_chunk_callback;
+}
+
+void TraceResultBuffer::Start() {
+  append_comma_ = false;
+  output_callback_.Run("[");
+}
+
+void TraceResultBuffer::AddFragment(const std::string& trace_fragment) {
+  if (append_comma_)
+    output_callback_.Run(",");
+  append_comma_ = true;
+  output_callback_.Run(trace_fragment);
+}
+
+void TraceResultBuffer::Finish() {
+  output_callback_.Run("]");
+}
+
+////////////////////////////////////////////////////////////////////////////////
+//
 // TraceLog
 //
 ////////////////////////////////////////////////////////////////////////////////