title: Flutter Problem with textformfield, the input does not center
body: <p>I have a problem with multiline chat input. When the user enter the chat, the input should be centered in the Container. However it is not the case and I can't fix it with padding.</p>
  
  <p>Here is the screenschot of what I get : 
  <a href="https://i.stack.imgur.com/C6qeK.jpg" rel="nofollow noreferrer">enter image description here</a></p>
  
  <p>What I should get instead :
  <a href="https://i.stack.imgur.com/JORQO.jpg" rel="nofollow noreferrer">enter image description here</a></p>
  
  <p>Here is the code :</p>
  
  <pre><code>Container(
              width: screenWidth - 130.0,
              height: 30.0,
              padding: EdgeInsets.fromLTRB(8.0, 0.0, 8.0, 0.0),
              decoration: BoxDecoration(
                  color: Colors.grey[200],
                  borderRadius: BorderRadius.circular(15.0)),
              child: new ConstrainedBox(
                constraints: BoxConstraints(maxHeight: 300.0),
                child: ScrollConfiguration(
                  behavior: DisableScrollGlow(),
                  child: new Scrollbar(
                    child: new SingleChildScrollView(
                      scrollDirection: Axis.vertical,
                      reverse: true,
                      child: Center(
                        child: new TextField(
                          keyboardType: TextInputType.text,
                          autofocus: true,
                          maxLines: null,
                          controller: _messageController,
                          decoration: InputDecoration(
                              contentPadding:
                              EdgeInsets.only(left: 0, bottom: 0.0, top: 0.0, right: 0),
                              enabledBorder: InputBorder.none,
                              errorBorder: InputBorder.none,
                              disabledBorder: InputBorder.none,
                              border: InputBorder.none,
                              focusedBorder: InputBorder.none),
                        ),
                      ),
                    ),
                  ),
                ),
              ),
            ),
  </code></pre>
  
  <p>All help is welcomed</p>