Avoid emptry tracing callbacks when possible.

base/trace_event/trace_event_impl.cc

Index: base/trace_event/trace_event_impl.cc
diff --git a/base/trace_event/trace_event_impl.cc b/base/trace_event/trace_event_impl.cc
index b5d4298e653027c20bfd52b7806aaac90f1e928a..5882333c1714385d343be54791629c67031772fa 100644
--- a/base/trace_event/trace_event_impl.cc
+++ b/base/trace_event/trace_event_impl.cc
@@ -1815,25 +1815,21 @@ void TraceLog::ConvertTraceEventsToTraceFormat(
 
   // The callback need to be called at least once even if there is no events
   // to let the caller know the completion of flush.
-  bool has_more_events = true;
-  do {
-    scoped_refptr<RefCountedString> json_events_str_ptr =
-        new RefCountedString();
-
-    while (json_events_str_ptr->size() < kTraceEventBufferSizeInBytes) {
-      const TraceBufferChunk* chunk = logged_events->NextChunk();
-      has_more_events = chunk != NULL;
-      if (!chunk)
-        break;
-      for (size_t j = 0; j < chunk->size(); ++j) {
-        if (json_events_str_ptr->size())
-          json_events_str_ptr->data().append(",\n");
-        chunk->GetEventAt(j)->AppendAsJSON(&(json_events_str_ptr->data()),
-                                           argument_filter_predicate);
+  scoped_refptr<RefCountedString> json_events_str_ptr = new RefCountedString();
+  while (const TraceBufferChunk* chunk = logged_events->NextChunk()) {
+    for (size_t j = 0; j < chunk->size(); ++j) {
+      size_t size = json_events_str_ptr->size();
+      if (size > kTraceEventBufferSizeInBytes) {
+        flush_output_callback.Run(json_events_str_ptr, true);
+        json_events_str_ptr = new RefCountedString();
+      } else if (size) {
+        json_events_str_ptr->data().append(",\n");
       }
+      chunk->GetEventAt(j)->AppendAsJSON(&(json_events_str_ptr->data()),
+                                         argument_filter_predicate);
     }
-    flush_output_callback.Run(json_events_str_ptr, has_more_events);
-  } while (has_more_events);
+  }
+  flush_output_callback.Run(json_events_str_ptr, false);
 }
 
 void TraceLog::FinishFlush(int generation) {