Only allow editable textfields to consume backspace.

Do not prevent accelerator handling by read only textfields.

BUG=374006
TEST=Backspace navigates back on when a popup omnibox or cookies dialog textfield is focused.
R=pkasting@chromium.org

Review URL: https://codereview.chromium.org/289183002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@271232 0039d316-1c4b-4281-b951-d872f2087c98

ui/views/controls/textfield/textfield.cc

@@ -724,9 +724,10 @@ bool Textfield::SkipDefaultKeyEventProcessing(const ui::KeyEvent& event) {
   }
 #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(