WebViewCompatible does not render as expected in designer

[rjmurillo]

I'm submitting a...

• Bug report (I searched for similar issues and did not find one)

Current behavior

When adding the WebViewCompatible to a WPF surface, the web page is rendered but not to the dimensions requested.

Expected behavior

When layout is set to Auto (default) for the control, the control should stretch into the available area. The behavior is as expected at runtime.

Minimal reproduction of the problem with instructions

WebViewCompatible_WPF_Designer_Size.zip

MainWindow.xaml

<Window xmlns:Controls="clr-namespace:Microsoft.Toolkit.Wpf.UI.Controls;assembly=Microsoft.Toolkit.Wpf.UI.Controls.WebView"  x:Class="WebViewCompatible.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WebViewCompatible"
        mc:Ignorable="d"
        Title="WebViewCompatible Browser" Height="450" Width="800">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="20"></RowDefinition>
            <RowDefinition></RowDefinition>
        </Grid.RowDefinitions>
        <StackPanel>
            <Grid>
                <Button HorizontalAlignment="Left" Click="OnBackClicked">Back</Button>
                <Label x:Name="LoadingLabel" HorizontalAlignment="Center" Visibility="Collapsed">Loading...</Label>
                <Button HorizontalAlignment="Right" Click="OnForwardClicked">Forward</Button>
            </Grid>
        </StackPanel>
        <Controls:WebViewCompatible Grid.Row="1" x:Name="Browser" Source="https://www.bing.com" NavigationStarting="BrowserNavigating" NavigationCompleted="BrowserNavigated" MinHeight="92" MinWidth="375" />
    </Grid>
</Window>

Environment

Nuget Package(s): Microsoft.Toolkit.Wpf.UI.Controls.WebView

Package Version(s): 4.1.0-build.83

Windows 10 Build Number:
- [ ] Creators Update (15063)
- [ ] Fall Creators Update (16299)
- [ ] April 2018 Update (17134)
- [x] Insider Build (build number: 18244)

App min and target version:
- [ ] Creators Update (15063)
- [ ] Fall Creators Update (16299)
- [ ] April 2018 Update (17134)
- [ ] Insider Build (xxxxx)

Device form factor:
- [x] Desktop
- [ ] Mobile
- [ ] Xbox
- [ ] Surface Hub
- [ ] IoT

Visual Studio 
- [x] 2017 (version: 15.8.4)
- [ ] 2017 Preview (version: )

[rjmurillo]

@joshholmes FYI