title: CustomScrollView slivers with contents in SliverFillRemaining not scrolling
body: <p>I am trying to create a flutter screen using the CustomScrollView and Sliver widgets where the SliverFillRemaining has a Text widget that can scroll down like reading scroll-able text content.</p>
  
  <p>I can achieve this by wrapping the Text within the SingleChildScrollView however i want to have the functionality of a header that can automatically hide using SliverAppBar</p>
  
  <p>How can i achieve the behaviour similar to SingleChildScrollView?</p>
  
  <p>When i add Text widget inside SliverFillRemaining it only scrolls down until the SliverAppBar is hidden and then stops.</p>
  
  <pre><code>var scaffold = Scaffold(
      body: CustomScrollView(
          slivers: &lt;Widget&gt;[
              SliverAppBar(
                  pinned: false,
                  snap: false,
                  floating: true,
                  expandedHeight: 40.0,
                  flexibleSpace: FlexibleSpaceBar(
                      title: Text(widget.path.title),
                  ),
              ),
              SliverFillRemaining(
                  hasScrollBody: true,
                  child: Scrollbar(
                      child: Text(
                          data, //this variable has a huge string.
                          textAlign: TextAlign.left,
                          style: new TextStyle(
                              height: 1.5,
                              fontFamily: widget.fontFamily,
                              fontSize: widget.fontSize,
                              fontWeight: (widget.bold)? FontWeight.bold:FontWeight.normal,
                          ),
                      ),
                  ),
              )
          ]
      ),
  </code></pre>