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

content/public/browser/trace_subscriber.h

Index: content/public/browser/trace_subscriber.h
diff --git a/content/public/browser/trace_subscriber.h b/content/public/browser/trace_subscriber.h
index 02e9f1cf35d279cec99493d3eba6e481fef244f4..4758f6f25174de75f1e1acaba362b59caef620c3 100644
--- a/content/public/browser/trace_subscriber.h
+++ b/content/public/browser/trace_subscriber.h
@@ -20,11 +20,16 @@ class TraceSubscriber {
   // Called once after TraceController::EndTracingAsync.
   virtual void OnEndTracingComplete() = 0;
 
+  // Called once after TraceController::ShowContinuousSamplingTracing.
+  virtual void OnShowContinuousSamplingTracingComplete() {}
+
   // Called 0 or more times between TraceController::BeginTracing and
   // OnEndTracingComplete. Use base::debug::TraceResultBuffer to convert one or
   // more trace fragments to JSON.
   virtual void OnTraceDataCollected(
       const scoped_refptr<base::RefCountedString>& trace_fragment) = 0;
+  virtual void OnContinuousSamplingTraceDataCollected(
+      const scoped_refptr<base::RefCountedString>& trace_fragment) {}
 
   // Called once after TraceController::GetKnownCategoryGroupsAsync.
   virtual void OnKnownCategoriesCollected(