Blink handle selection handle visibility

cc/proto/layer_selection_bound.proto

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 syntax = "proto2";
 
 import "point.proto";
 
 option optimize_for = LITE_RUNTIME;
 
@@ skipping 12 matching lines @@
   optional Point edge_top = 2;
   optional Point edge_bottom = 3;
   optional int32 layer_id = 4;
 }
 
 message LayerSelection {
   optional LayerSelectionBound start = 1;
   optional LayerSelectionBound end = 2;
   optional bool is_editable = 3;
   optional bool is_empty_text_form_control = 4;
+  optional bool is_handle_visible = 5;
 }