Update tracing framework to optionally use a ringbuffer.

content/public/browser/trace_controller.h

Index: content/public/browser/trace_controller.h
diff --git a/content/public/browser/trace_controller.h b/content/public/browser/trace_controller.h
index 6bdff6c0c13d7c1c0d51a8bd6b7f8282d8bc42b5..a9be3b489f0ae5f1043208f3ec360cb66c596a02 100644
--- a/content/public/browser/trace_controller.h
+++ b/content/public/browser/trace_controller.h
@@ -35,12 +35,19 @@ class TraceController {
   // All the same rules apply above, so for example, having both included and
   // excluded categories in the same list would not be supported.
   //
+  // |continuous_tracing| should be set to true to loop to the beginning of
+  // the trace buffer and continue tracing when the buffer is full.
+  //
   // Example: BeginTracing("test_MyTest*");
   // Example: BeginTracing("test_MyTest*,test_OtherStuff");
   // Example: BeginTracing("-excluded_category1,-excluded_category2");
   virtual bool BeginTracing(TraceSubscriber* subscriber,
                             const std::string& categories) = 0;
 
+  virtual bool BeginTracing(TraceSubscriber* subscriber,
+                            const std::string& categories,
+                            bool continuous_tracing) = 0;
+
   // Called by browser process to stop tracing events on all processes.
   //
   // Child processes typically are caching trace data and only rarely flush