Make TypingCommand::insertText() to take SelectionInDOMTree instead of VisibleSelection

This patch makes |TypingCommand::insertText()| to take |SelectionInDOMTree|
instead of |VisibleSelection| to reduce usage of |VisibleSelection| for
improving code health.

BUG=657237
TEST=n/a

Review-Url: https://codereview.chromium.org/2733183002
Cr-Commit-Position: refs/heads/master@{#455368}
InputEvent::EventIsComposing isComposingFromCommand(
    const CompositeEditCommand* command) {
  if (command->isTypingCommand() &&
      toTypingCommand(command)->compositionType() !=
          TypingCommand::TextCompositionNone)
    return InputEvent::EventIsComposing::IsComposing;
  return InputEvent::EventIsComposing::NotComposing;
}

InputEvent::EventIsComposing isComposingFromCommand(
    const CompositeEditCommand* command) {
  if (command->isTypingCommand() &&
      toTypingCommand(command)->compositionType() !=
          TypingCommand::TextCompositionNone)
    return InputEvent::EventIsComposing::IsComposing;
  return InputEvent::EventIsComposing::NotComposing;
}
