[debugger] fix debug-evaluate wrt shadowed context var.

src/debug/debug-frames.cc

Index: src/debug/debug-frames.cc
diff --git a/src/debug/debug-frames.cc b/src/debug/debug-frames.cc
index ad54247417ddad2b36ca3b02bf578de783267f1f..29f7d3cac550fac248e688833199f8039a883ca3 100644
--- a/src/debug/debug-frames.cc
+++ b/src/debug/debug-frames.cc
@@ -109,6 +109,8 @@ void FrameInspector::MaterializeStackLocals(Handle<JSObject> target,
   // First fill all parameters.
   for (int i = 0; i < scope_info->ParameterCount(); ++i) {
     // Do not materialize the parameter if it is shadowed by a context local.
+    // TODO(yangguo): check whether this is necessary, now that we materialize
+    //                context locals as well.
     Handle<String> name(scope_info->ParameterName(i));
     if (ParameterIsShadowedByContextLocal(scope_info, name)) continue;