Update tracing framework to optionally use a ringbuffer.

content/browser/tracing/tracing_ui.cc

Index: content/browser/tracing/tracing_ui.cc
diff --git a/content/browser/tracing/tracing_ui.cc b/content/browser/tracing/tracing_ui.cc
index b82da36160152477d17794866864a1b93f497bde..069c2b9c8b54dc09c21312b1710ae34854cd883b 100644
--- a/content/browser/tracing/tracing_ui.cc
+++ b/content/browser/tracing/tracing_ui.cc
@@ -370,7 +370,8 @@ void TracingMessageHandler::SaveTraceFileComplete() {
 
 void TracingMessageHandler::OnBeginTracing(const ListValue* args) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
-  DCHECK_EQ(args->GetSize(), (size_t) 2);
+  DCHECK_GE(args->GetSize(), (size_t) 2);
+  DCHECK_LE(args->GetSize(), (size_t) 3);
 
   bool system_tracing_requested = false;
   bool ok = args->GetBoolean(0, &system_tracing_requested);
@@ -380,12 +381,19 @@ void TracingMessageHandler::OnBeginTracing(const ListValue* args) {
   ok = args->GetString(1, &chrome_categories);
   DCHECK(ok);
 
+  bool continuous_tracing = false;
+  if (args->GetSize() == 3) {
+    ok = args->GetBoolean(2, &continuous_tracing);
+    DCHECK(ok);
+  }
+
   trace_enabled_ = true;
   // TODO(jbates) This may fail, but that's OK for current use cases.
   //              Ex: Multiple about:gpu traces can not trace simultaneously.
   // TODO(nduca) send feedback to javascript about whether or not BeginTracing
   //             was successful.
-  TraceController::GetInstance()->BeginTracing(this, chrome_categories);
+  TraceController::GetInstance()->BeginTracing(this, chrome_categories,
+                                               continuous_tracing);
 
   if (system_tracing_requested) {
 #if defined(OS_CHROMEOS)