[Startup Tracing] Remove |is_recording_| in devtool tracing_handler

content/public/browser/tracing_controller.h

Index: content/public/browser/tracing_controller.h
diff --git a/content/public/browser/tracing_controller.h b/content/public/browser/tracing_controller.h
index 9c68fcf3c8dc3ab016136f03362b3a2fa6708f81..45c2ce024469171f2b9cd6b14b43aaed143c8715 100644
--- a/content/public/browser/tracing_controller.h
+++ b/content/public/browser/tracing_controller.h
@@ -199,6 +199,9 @@ class TracingController {
   // watch event callback.
   virtual bool CancelWatchEvent() = 0;
 
+  // Check if the tracing system is recording
+  virtual bool IsRecording() const = 0;
+
  protected:
   virtual ~TracingController() {}
 };