[interpreter, debugger] abstraction for source position calculation.

src/accessors.cc

Index: src/accessors.cc
diff --git a/src/accessors.cc b/src/accessors.cc
index bcc4f05c0937c4ad95bd06e4e6ff3b36ec7a5414..f4eff3b732e98a90ddc3f5155f774b1918d4e556 100644
--- a/src/accessors.cc
+++ b/src/accessors.cc
@@ -663,7 +663,6 @@ void Accessors::ScriptEvalFromScriptPositionGetter(
     Handle<Code> code(SharedFunctionInfo::cast(
         script->eval_from_shared())->code());
     result = Handle<Object>(Smi::FromInt(code->SourcePosition(
-                                code->instruction_start() +
                                 script->eval_from_instructions_offset())),
                             isolate);
   }