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..0fcdaf853b5d95f9d9b6c87c302ac74c88973ac9 100644
--- a/base/debug/trace_event.cc
+++ b/base/debug/trace_event.cc
@@ -224,13 +224,11 @@ 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 +260,32 @@ void TraceEvent::AppendAsJSON(std::string* out) const {
 
 ////////////////////////////////////////////////////////////////////////////////
 //
+// TraceResultBuffer
+//
+////////////////////////////////////////////////////////////////////////////////
+
+TraceResultBuffer::TraceResultBuffer() {
+}
+
+TraceResultBuffer::~TraceResultBuffer() {
+}
+
+void TraceResultBuffer::AddFragment(const std::string& trace_fragment) {
+  fragments_.push_back(trace_fragment);
+}
+
+void TraceResultBuffer::GetJSON(std::string* json_trace_output) {
+  *json_trace_output = "[";
+  for (size_t i = 0; i < fragments_.size(); ++i) {

[nduca, 2011/10/20 00:28:03]

Algorithmically, I see a bit too many strdups. I'd <3 to see this do:

std::string result_; bool terminated_;
constructor: result_("["), terminated_(false);
addfragment: DCHECK(!terminated_); result_ += trace_fragment; result_ += ",";
getJSON() {
  if(!terminated_) {
    terminated_ = true;
    result += "]";
  }
  return result_;
}

bonus points for unterminating instead of dchecking.

Less strduping == good, yes?

[jbates, 2011/10/20 22:18:49]

Similar optimizations occurred to me, but I thought performance was not
important here so not worth the design complication / code maintenance. Ah well!
Done.

+    if (i > 0)
+      *json_trace_output += ",";
+    *json_trace_output += fragments_[i];
+  }
+  *json_trace_output += "]";
+}
+
+////////////////////////////////////////////////////////////////////////////////
+//
 // TraceLog
 //
 ////////////////////////////////////////////////////////////////////////////////