c# - 別のグリッド内でのグリッドのストレッチ

Question

「SecondGrid」を水平方向に伸ばすにはどうすればよいですか?

<Window x:Class="WpfApplication2.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MainWindow" Height="350" Width="525">
<Grid VerticalAlignment="Stretch" HorizontalAlignment="Stretch">
    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="*"/>
        <ColumnDefinition Width="Auto"/>
        <ColumnDefinition Width="*"/>
    </Grid.ColumnDefinitions>
    <Label Content="Left" Grid.Column="0" />
    <GridSplitter HorizontalAlignment="Right" 
              VerticalAlignment="Stretch" 
              Grid.Column="1" ResizeBehavior="PreviousAndNext"
              Width="5" Background="#FFBCBCBC"/>
    <Label Content="Righkk" Grid.Column="2" Margin="5,0,-5,0" />


    <Grid Name="SecondGrid" Grid.Column="2" HorizontalAlignment="Stretch" VerticalAlignment="Stretch">
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="*" />
            <ColumnDefinition Width="Auto" />
            <ColumnDefinition Width="*"  />
        </Grid.ColumnDefinitions>
        <Grid.RowDefinitions>
            <RowDefinition Height="*" />
            <RowDefinition Height="Auto" />
            <RowDefinition Height="*" />
        </Grid.RowDefinitions>

        <GridSplitter 
        ResizeDirection="Rows"            
        Grid.Row="1"
        Width="Auto" 
        Height="3"
       Background="#FFBCBCBC"
        HorizontalAlignment="Stretch" 
        />
        <ListBox HorizontalAlignment="Stretch"  VerticalAlignment="Stretch" Grid.Row="0"/>
        <WebBrowser  Grid.Row="2" HorizontalAlignment="Stretch" VerticalAlignment="Stretch"/>
        <Label Content="Right" Grid.Row="2" />
    </Grid>


    <StackPanel HorizontalAlignment="Stretch" VerticalAlignment="Stretch">
        <ToolBarTray DockPanel.Dock="Top">
            <ToolBar>
                <Button Command="New" Content="New" />
                <Button Command="Open" Content="Open" />
                <Button Command="Save" Content="Save" />
            </ToolBar>
        </ToolBarTray>
        <TreeView>
            <TreeViewItem Header="Level 1" IsExpanded="True">
                <TreeViewItem Header="Level 2.1" />
                <TreeViewItem Header="Level 2.2" IsExpanded="True">
                    <TreeViewItem Header="Level 3.1" />
                    <TreeViewItem Header="Level 3.2" />
                </TreeViewItem>
                <TreeViewItem Header="Level 2.3" />
            </TreeViewItem>
        </TreeView>
    </StackPanel>

</Grid>