Add an API for additional profile log records

src/log.h

Index: src/log.h
===================================================================
--- src/log.h	(revision 16936)
+++ src/log.h	(working copy)
@@ -110,6 +110,7 @@
   V(SNAPSHOT_CODE_NAME_EVENT,       "snapshot-code-name")               \
   V(TICK_EVENT,                     "tick")                             \
   V(REPEAT_META_EVENT,              "repeat")                           \
+  V(MARK_EVENT,                     "mark")                             \
   V(BUILTIN_TAG,                    "Builtin")                          \
   V(CALL_DEBUG_BREAK_TAG,           "CallDebugBreak")                   \
   V(CALL_DEBUG_PREPARE_STEP_IN_TAG, "CallDebugPrepareStepIn")           \
@@ -277,6 +278,8 @@
   void CodeNameEvent(Address addr, int pos, const char* code_name);
   void SnapshotPositionEvent(Address addr, int pos);
 
+  void MarkEvent(char* mark);
+
   // ==== Events logged by --log-gc. ====
   // Heap sampling events: start, end, and individual types.
   void HeapSampleBeginEvent(const char* space, const char* kind);