[generators] Implement %GeneratorGetSourcePosition.

src/runtime/runtime-generator.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/runtime/runtime-utils.h"
 
 #include "src/arguments.h"
 #include "src/debug/debug.h"
 #include "src/factory.h"
 #include "src/frames-inl.h"
@@ skipping 128 matching lines @@
   return Smi::FromInt(generator->continuation());
 }
 
 
 RUNTIME_FUNCTION(Runtime_GeneratorGetSourcePosition) {
   HandleScope scope(isolate);
   DCHECK(args.length() == 1);
   CONVERT_ARG_HANDLE_CHECKED(JSGeneratorObject, generator, 0);
 
   if (!generator->is_suspended()) return isolate->heap()->undefined_value();
-
-  if (generator->function()->shared()->HasBytecodeArray()) UNIMPLEMENTED();
-
-  Handle<Code> code(generator->function()->code(), isolate);
-  int offset = generator->continuation();
-  CHECK(0 <= offset && offset < code->instruction_size());
-  return Smi::FromInt(code->SourcePosition(offset));
+  return Smi::FromInt(generator->source_position());
 }
 
 }  // namespace internal
 }  // namespace v8