Verify that previous_selected_line is within bounds before passing to

chrome/browser/ui/autofill/autofill_popup_controller_impl.cc

 // Copyright (c) 2012 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.
 
 #include "chrome/browser/ui/autofill/autofill_popup_controller_impl.h"
 
 #include <algorithm>
 #include <utility>
 
 #include "base/command_line.h"
@@ skipping 341 matching lines @@
   if (!delegate_->RemoveSuggestion(suggestions_[list_index].value,
                                    suggestions_[list_index].frontend_id)) {
     return false;
   }
 
   // Remove the deleted element.
   suggestions_.erase(suggestions_.begin() + list_index);
   elided_values_.erase(elided_values_.begin() + list_index);
   elided_labels_.erase(elided_labels_.begin() + list_index);
 
   SetSelectedLine(base::nullopt);

[Evan Stade, 2017/03/23 23:06:49]

this is the problem, right? Can we change this line to selected_line_.reset()?

we're doing a lot of excess work (repaints, ClearPreviewedForm x 2) by calling
SetSelectedLine.

[csashi, 2017/03/23 23:45:25]

Done. Thanks for the suggestion. To the best of my verification, the effect is
the same minus the bug and is simpler.

 
   if (HasSuggestions()) {
     delegate_->ClearPreviewedForm();
     OnSuggestionsChanged();
   } else {
     Hide();
   }
 
   return true;
 }
@@ skipping 18 matching lines @@
     base::Optional<int> selected_line) {
   if (selected_line_ == selected_line)
     return;
 
   if (selected_line) {
     DCHECK_LT(*selected_line, GetLineCount());
     if (!CanAccept(suggestions_[*selected_line].frontend_id))
       selected_line = base::nullopt;
   }
 
-  auto previous_selected_line(selected_line_);
+  base::Optional<int> previous_selected_line;
+  if (selected_line_ && *selected_line_ < suggestions_.size()) {
+    previous_selected_line = selected_line_;
+  }
+
   selected_line_ = selected_line;
   view_->OnSelectedRowChanged(previous_selected_line, selected_line_);
 
   if (selected_line_) {
     delegate_->DidSelectSuggestion(suggestions_[*selected_line_].value,
                                    suggestions_[*selected_line_].frontend_id);
   } else {
     delegate_->ClearPreviewedForm();
   }
 }
@@ skipping 100 matching lines @@
   // Don't clear view_, because otherwise the popup will have to get regenerated
   // and this will cause flickering.
   suggestions_.clear();
   elided_values_.clear();
   elided_labels_.clear();
 
   selected_line_.reset();
 }
 
 }  // namespace autofill