[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..4a511849378394b39b8c5722f94d0c209c7c53af 100644
--- a/include/v8-platform.h
+++ b/include/v8-platform.h
@@ -7,6 +7,8 @@
 
 #include <stddef.h>
 #include <stdint.h>
+#include <memory>
+#include <string>
 
 namespace v8 {
 
@@ -17,24 +19,38 @@ 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 +70,7 @@ class Platform {
     kLongRunningTask
   };
 
-  virtual ~Platform() {}
+  virtual ~Platform() = default;
 
   /**
    * Gets the number of threads that are used to execute background tasks. Is
@@ -159,6 +175,24 @@ class Platform {
   }
 
   /**
+   * Adds a trace event to the platform tracing system. This function call is
+   * usually the result of a TRACE_* macro from trace_event_common.h when
+   * tracing and the category of the particular trace are enabled. It is not
+   * advisable to call this function on its own; it is really only meant to be
+   * used by the trace macros. The returned handle can be used by
+   * UpdateTraceEventDuration to update the duration of COMPLETE events.
+   */
+  virtual uint64_t AddTraceEvent(
+      char phase, const uint8_t* category_enabled_flag, const char* name,
+      const char* scope, uint64_t id, uint64_t bind_id, int32_t num_args,
+      const char** arg_names, const uint8_t* arg_types,
+      const uint64_t* arg_values,
+      std::unique_ptr<ConvertableToTraceFormat>* arg_convertables,
+      unsigned int flags) {
+    return 0;

[caseq, 2016/09/23 23:48:34]

call another one here instead, so that when the embedder implements this one,
another one is not called.

[alph, 2016/09/24 00:24:06]

Done.

+  }
+
+  /**
    * Sets the duration field of a COMPLETE trace event. It must be called with
    * the handle returned from AddTraceEvent().
    **/