title: Office UI Fabric React - ComboBox - first tap dismiss issue on mobile
body: <p>I am using office-ui-fabric-react: 7.160.2 like this</p>
  <pre><code>                    &lt;ComboBox
                        required={true}
                        key={key}
                        autoComplete=&quot;on&quot;
                        allowFreeform={true}
                        options={options}
                        selectedKey={selectedKey}
                        defaultSelectedKey={defaultSelectedKey}
                        onChange={this.handleOnChange}
                        styles={comboBoxStyle}
                        useComboBoxAsMenuWidth={true}
                      /&gt;
  </code></pre>
  <p>And I have an issue when using on mobile.
  First tap on dropdown icon -&gt; show dropdown -&gt; input auto focus -&gt; display keyboard -&gt; dropdown dismiss. I need tap one more time after that to show dropdown</p>
  <p>Anyone meet this issue? And how to solve that? Or how to prevent auto focus after tap to dropdown icon?</p>
  <p>Thank all</p>