Internalize JSON chunk management to trace_event.h API.

content/browser/trace_subscriber_stdio.cc

Index: content/browser/trace_subscriber_stdio.cc
diff --git a/content/browser/trace_subscriber_stdio.cc b/content/browser/trace_subscriber_stdio.cc
index bf6a8fccd2adc84ad88e86535eaf5a7495d81ce7..901aea09b100ccc361084be445a501d672ada280 100644
--- a/content/browser/trace_subscriber_stdio.cc
+++ b/content/browser/trace_subscriber_stdio.cc
@@ -4,6 +4,7 @@
 
 #include "content/browser/trace_subscriber_stdio.h"
 
+#include "base/bind.h"
 #include "base/logging.h"
 
 TraceSubscriberStdio::TraceSubscriberStdio() : file_(0) {
@@ -22,8 +23,9 @@ bool TraceSubscriberStdio::OpenFile(const FilePath& path) {
   CloseFile();
   file_ = file_util::OpenFile(path, "w+");
   if (IsValid()) {
-    // FIXME: the file format expects it to start with "[".
-    fputc('[', file_);
+    trace_buffer_.SetOutputCallback(base::Bind(&TraceSubscriberStdio::Write,
+                                               base::Unretained(this)));
+    trace_buffer_.Start();
     return true;
   } else {
     LOG(ERROR) << "Failed to open performance trace file: " << path.value();
@@ -33,8 +35,6 @@ bool TraceSubscriberStdio::OpenFile(const FilePath& path) {
 
 void TraceSubscriberStdio::CloseFile() {
   if (file_) {
-    // FIXME: the file format expects it to end with "]".
-    fputc(']', file_);
     fclose(file_);
     file_ = 0;
   }
@@ -45,27 +45,21 @@ bool TraceSubscriberStdio::IsValid() {
 }
 
 void TraceSubscriberStdio::OnEndTracingComplete() {
+  trace_buffer_.Finish();
   CloseFile();
 }
 
 void TraceSubscriberStdio::OnTraceDataCollected(
-    const std::string& json_events) {
-  if (!IsValid()) {
-    return;
-  }
-
-  // FIXME: "json_events" currently comes with "[" and "]". But the file doesn't
-  // expect them. So remove them when writing to the file.
-  CHECK_GE(json_events.size(), 2u);
-  const char* data = json_events.data() + 1;
-  size_t size = json_events.size() - 2;
+    const std::string& trace_fragment) {
+  trace_buffer_.AddFragment(trace_fragment);
+}
 
-  size_t written = fwrite(data, 1, size, file_);
-  if (written != size) {
-    LOG(ERROR) << "Error " << ferror(file_) << " when writing to trace file";
-    fclose(file_);
-    file_ = 0;
-  } else {
-    fputc(',', file_);
+void TraceSubscriberStdio::Write(const std::string& output_str) {
+  if (IsValid()) {
+    size_t written = fwrite(output_str.c_str(), 1, output_str.size(), file_);
+    if (written != output_str.size()) {
+      LOG(ERROR) << "Error " << ferror(file_) << " when writing to trace file";
+      CloseFile();
+    }
   }
 }