Record Chrome trace events in tcmalloc heap profiles

third_party/tcmalloc/chromium/src/gperftools/heap-profiler.h

 /* Copyright (c) 2005, Google Inc.
  * All rights reserved.
  * 
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  * 
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 50 matching lines @@
 # endif
 #endif
 
 /* All this code should be usable from within C apps. */
 #ifdef __cplusplus
 extern "C" {
 #endif
 
 /* Start profiling and arrange to write profile data to file names
  * of the form: "prefix.0000", "prefix.0001", ...
+ * |prefix| may be NULL, which prevents writing to disk. This is useful for
+ * applications that exclusively use GetHeapProfile().

[Dai Mikurube (NOT FULLTIME), 2013/06/19 04:34:03]

This comment looks confusing.  The existing profiler assumes that the profiler
is turned off if filename_prefix == NULL.

The comment should explicitly describe which function is allowed, and which
function is disallowed in case of |prefix| == NULL.  E.g. "No writing to disk
while profiling is started if |prefix| == NULL. GetHeapProfile() and ???() are
available, but ???() and ???() cannot be used."  (My English statement might be
improved, though. ;))

[James Cook, 2013/06/29 00:02:42]

Updated the comment. I think the system considers profiling off when |is_on| is
false?  Also, this should be a little clearer now that I'm using
HeapProfilerWithPseudoStackStart().

  */
 PERFTOOLS_DLL_DECL void HeapProfilerStart(const char* prefix);
 
 /* Returns non-zero if we are currently profiling the heap.  (Returns
  * an int rather than a bool so it's usable from C.)  This is true
  * between calls to HeapProfilerStart() and HeapProfilerStop(), and
  * also if the program has been run with HEAPPROFILER, or some other
  * way to turn on whole-program profiling.
  */
 int IsHeapProfilerRunning();
@@ skipping 21 matching lines @@
  * to the object being visited.
  */
 typedef void (*AddressVisitor)(void* data, const void* ptr);
 
 /* Iterate over all live allocated objects. For each allocation the
  * callback will be invoked with the data argument and allocation pointer.
  */
 PERFTOOLS_DLL_DECL void IterateAllocatedObjects(AddressVisitor callback,
                                                 void* data);
 
+/* Sets a callback function to return a pseudo-stack for application-generated
+ * stacks during heap profiling. The caller must provide a buffer in |stack|
+ * of at least size 32 * sizeof(void*). Returns the number of items copied or
+ * zero.
+ */
+typedef int (*PseudoStackGenerator)(void** stack);
+PERFTOOLS_DLL_DECL void SetPseudoStackGenerator(PseudoStackGenerator callback);
+
 #ifdef __cplusplus
 }  // extern "C"
 #endif
 
 #endif  /* BASE_HEAP_PROFILER_H_ */