Implement about:tracing UI for the sampling profiler (Chromium part)

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 0049555a9963d12d0946150846216c81b2f55b52..5aa058ad507af3abe11198744e558e2e77661d49 100644
--- a/content/public/browser/trace_controller.h
+++ b/content/public/browser/trace_controller.h
@@ -62,6 +62,11 @@ class TraceController {
   //   EndTracingAsync will return false meaning it failed.
   virtual bool EndTracingAsync(TraceSubscriber* subscriber) = 0;
 
+  virtual bool BeginContinuousSamplingTracing(TraceSubscriber* subscriber) = 0;
+  virtual bool EndContinuousSamplingTracing(TraceSubscriber* subscriber) = 0;
+  virtual bool ShowContinuousSamplingTracingAsync(
+      TraceSubscriber* subscriber) = 0;
+
   // Get the maximum across processes of trace buffer percent full state.
   // When the TraceBufferPercentFull value is determined,
   // subscriber->OnTraceBufferPercentFullReply is called.