Only allow editable textfields to consume backspace.

ui/views/controls/textfield/textfield.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 "ui/views/controls/textfield/textfield.h"
 
 #include <string>
 
 #include "base/debug/trace_event.h"
 #include "grit/ui_strings.h"
@@ skipping 706 matching lines @@
       ui::GetTextEditKeyBindingsDelegate();
   std::vector<ui::TextEditCommandAuraLinux> commands;
   if (delegate && delegate->MatchEvent(event, &commands)) {
     const bool rtl = GetTextDirection() == base::i18n::RIGHT_TO_LEFT;
     for (size_t i = 0; i < commands.size(); ++i)
       if (IsCommandIdEnabled(GetViewsCommand(commands[i], rtl)))
         return true;
   }
 #endif
 
-  // Skip any accelerator handling of backspace; textfields handle this key.
+  // Skip backspace accelerator handling; editable textfields handle this key.
   // Also skip processing Windows [Alt]+<num-pad digit> Unicode alt-codes.
-  return event.key_code() == ui::VKEY_BACK || event.IsUnicodeKeyCode();
+  const bool is_backspace = event.key_code() == ui::VKEY_BACK;
+  return (is_backspace && !read_only()) || event.IsUnicodeKeyCode();
 }
 
 bool Textfield::GetDropFormats(
     int* formats,
     std::set<OSExchangeData::CustomFormat>* custom_formats) {
   if (!enabled() || read_only())
     return false;
   // TODO(msw): Can we support URL, FILENAME, etc.?
   *formats = ui::OSExchangeData::STRING;
   if (controller_)
@@ skipping 940 matching lines @@
       const size_t length = selection_clipboard_text.length();
       range = gfx::Range(range.start() + length, range.end() + length);
     }
     model_->MoveCursorTo(gfx::SelectionModel(range, affinity));
     UpdateAfterChange(true, true);
     OnAfterUserAction();
   }
 }
 
 }  // namespace views