[tracing] Support ConvertableToTraceFormat argument type.

include/v8-platform.h

Index: include/v8-platform.h
diff --git a/include/v8-platform.h b/include/v8-platform.h
index d0b7aed8fc5a333bbef5281f8969db521e91c7af..e9006465e0d27cb59a8bd61029e14b9ffeb62f56 100644
--- a/include/v8-platform.h
+++ b/include/v8-platform.h
@@ -7,6 +7,7 @@
 
 #include <stddef.h>
 #include <stdint.h>
+#include <string>
 
 namespace v8 {
 
@@ -17,24 +18,38 @@ class Isolate;
  */
 class Task {
  public:
-  virtual ~Task() {}
+  virtual ~Task() = default;
 
   virtual void Run() = 0;
 };
 
-
 /**
-* An IdleTask represents a unit of work to be performed in idle time.
-* The Run method is invoked with an argument that specifies the deadline in
-* seconds returned by MonotonicallyIncreasingTime().
-* The idle task is expected to complete by this deadline.
-*/
+ * An IdleTask represents a unit of work to be performed in idle time.
+ * The Run method is invoked with an argument that specifies the deadline in
+ * seconds returned by MonotonicallyIncreasingTime().
+ * The idle task is expected to complete by this deadline.
+ */
 class IdleTask {
  public:
-  virtual ~IdleTask() {}
+  virtual ~IdleTask() = default;
   virtual void Run(double deadline_in_seconds) = 0;
 };
 
+/**
+ * The interface represents complex arguments to trace events.
+ */
+class ConvertableToTraceFormat {
+ public:
+  virtual ~ConvertableToTraceFormat() = default;
+
+  /**
+   * Append the class info to the provided |out| string. The appended
+   * data must be a valid JSON object. Strings must be properly quoted, and
+   * escaped. There is no processing applied to the content after it is
+   * appended.
+   */
+  virtual void AppendAsTraceFormat(std::string* out) const = 0;
+};
 
 /**
  * V8 Platform abstraction layer.
@@ -54,7 +69,7 @@ class Platform {
     kLongRunningTask
   };
 
-  virtual ~Platform() {}
+  virtual ~Platform() = default;
 
   /**
    * Gets the number of threads that are used to execute background tasks. Is