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

src/debug/debug-frames.cc

 // Copyright 2015 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/debug/debug-frames.h"
 
 #include "src/frames-inl.h"
 
 namespace v8 {
 namespace internal {
@@ skipping 91 matching lines @@
 
 
 // Create a plain JSObject which materializes the local scope for the specified
 // frame.
 void FrameInspector::MaterializeStackLocals(Handle<JSObject> target,
                                             Handle<ScopeInfo> scope_info) {
   HandleScope scope(isolate_);
   // 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;
 
     Handle<Object> value(i < GetParametersCount()
                              ? GetParameter(i)
                              : isolate_->heap()->undefined_value(),
                          isolate_);
     DCHECK(!value->IsTheHole());
 
     JSObject::SetOwnPropertyIgnoreAttributes(target, name, value, NONE).Check();
@@ skipping 87 matching lines @@
       if (!frames[i].function()->shared()->IsSubjectToDebugging()) continue;
       if (++count == index) return i;
     }
   }
   return -1;
 }
 
 
 }  // namespace internal
 }  // namespace v8