[interpreter, debugger] abstraction for source position calculation.

src/runtime/runtime-generator.cc

Index: src/runtime/runtime-generator.cc
diff --git a/src/runtime/runtime-generator.cc b/src/runtime/runtime-generator.cc
index 54894a013a624d287fe4efe03e04bbc678410527..a718fcc7f8af317eca45b7dd10433b2de53a7a4d 100644
--- a/src/runtime/runtime-generator.cc
+++ b/src/runtime/runtime-generator.cc
@@ -195,11 +195,8 @@ RUNTIME_FUNCTION(Runtime_GeneratorGetSourcePosition) {
   if (generator->is_suspended()) {
     Handle<Code> code(generator->function()->code(), isolate);
     int offset = generator->continuation();
-
-    RUNTIME_ASSERT(0 <= offset && offset < code->Size());
-    Address pc = code->address() + offset;
-
-    return Smi::FromInt(code->SourcePosition(pc));
+    RUNTIME_ASSERT(0 <= offset && offset < code->instruction_size());
+    return Smi::FromInt(code->SourcePosition(offset));
   }
 
   return isolate->heap()->undefined_value();