Merge the Merlin heap tracing to top-of-trunk.

runtime/include/dart_api.h

Index: runtime/include/dart_api.h
diff --git a/runtime/include/dart_api.h b/runtime/include/dart_api.h
index ad3fa48e85c212016d5040ee09607c7063403b36..2c09ed6697b1fb862922d0e44b34729bde4799fa 100755
--- a/runtime/include/dart_api.h
+++ b/runtime/include/dart_api.h
@@ -534,12 +534,17 @@ DART_EXPORT Dart_Handle Dart_RemoveGcEpilogueCallback(
 // --- Heap Profiler ---
 
 /**
- * A callback invoked by the heap profiler during profiling to write
- * data.
+ * A callback invoked by the VM to write to a specified stream.
+ * Used by the heap profiler and gc trace.
  */
-typedef void (*Dart_HeapProfileWriteCallback)(const void* data,
-                                              intptr_t length,
-                                              void* stream);
+typedef void (*Dart_FileWriteCallback)(const void* data,
+                                       intptr_t length,
+                                       void* stream);
+
+typedef void* (*Dart_FileOpenCallback)(const char* name);
+
+typedef void (*Dart_FileCloseCallback)(void* stream);
+
 
 /**
  * Generates a heap profile.
@@ -551,7 +556,7 @@ typedef void (*Dart_HeapProfileWriteCallback)(const void* data,
  *
  * \return Success if the heap profile is successful.
  */
-DART_EXPORT Dart_Handle Dart_HeapProfile(Dart_HeapProfileWriteCallback callback,
+DART_EXPORT Dart_Handle Dart_HeapProfile(Dart_FileWriteCallback callback,
                                          void* stream);
 
 // --- Initialization and Globals ---
@@ -2740,7 +2745,7 @@ DART_EXPORT Dart_Handle Dart_SetNativeResolver(
     Dart_NativeEntryResolver resolver);
 // TODO(turnidge): Rename to Dart_LibrarySetNativeResolver?
 
-// --- Profiling support ----
+// --- Profiling support ---
 
 // External pprof support for gathering and dumping symbolic
 // information that can be used for better profile reports for
@@ -2753,6 +2758,13 @@ typedef void (*Dart_FileWriterFunction)(const char* buffer, int64_t num_bytes);
 // Support for generating symbol maps for use by the Linux perf tool.
 DART_EXPORT void Dart_InitPerfEventsSupport(Dart_FileWriterFunction function);
 
+// --- Heap tracing support ---
+
+DART_EXPORT void Dart_InitHeapTrace(Dart_FileOpenCallback open_function,

[Ivan Posva, 2012/12/04 16:32:52]

Shouldn't we just register a general open, write and close callback? And then
init heap trace or the other operations with a name?

[cshapiro, 2012/12/04 21:13:33]

Sure, I can do that.  I would like the streams for the heap trace to do I/O
asynchronously.  This might be okay for other kinds of I/O but I am not entirely
certain.

+                                    Dart_FileWriteCallback write_function,
+                                    Dart_FileCloseCallback close_function,
+                                    const char* prefix);
+
 // --- Peers ---
 
 /**