This patch is the propagation version of https://codereview.chromium.org/10824032 patch

src/assembler.h

Index: src/assembler.h
===================================================================
--- src/assembler.h	(revision 13419)
+++ src/assembler.h	(working copy)
@@ -842,6 +842,7 @@
 #ifdef ENABLE_GDB_JIT_INTERFACE
     gdbjit_lineinfo_ = NULL;
 #endif
+    user_data_ = NULL;

[danno, 2013/02/01 13:43:10]

please call this (and all names of variables derived from it) jit_handler_data_

   }
 
 #ifdef ENABLE_GDB_JIT_INTERFACE
@@ -861,7 +862,15 @@
     return lineinfo;
   }
 #endif
+  void InitializeUserData(void* user_data) {

[danno, 2013/02/01 13:43:10]

AttachJITHandlerData?

+    user_data_ = user_data;
+  }
 
+  void* DetachJITLineInfo() {

[danno, 2013/02/01 13:43:10]

DetachJITHandlerData?

+    void* old_user_data = user_data_;
+    user_data_ = NULL;
+    return old_user_data;
+  }
   // Set current position to pos.
   void RecordPosition(int pos);
 
@@ -877,13 +886,18 @@
     return state_.current_statement_position;
   }
 
+  Assembler* assembler() {
+    return assembler_;
+  }
+
  private:
   Assembler* assembler_;
   PositionState state_;
 #ifdef ENABLE_GDB_JIT_INTERFACE
   GDBJITLineInfo* gdbjit_lineinfo_;
 #endif
-
+  // Currently user_data_ is used to keep the JITted code line info.

[danno, 2013/02/01 13:43:10]

I don't think this comment is exactly correct. It is used to store
JITHandler-specific data over the lifetime of a PositionsRecorder.

+  void* user_data_;
   friend class PreservePositionScope;
 
   DISALLOW_COPY_AND_ASSIGN(PositionsRecorder);