fixes

* proguard.cfg needed to prevent runtime crash (even with dx + proguard)
* fixes for r8

Author: jonathanpeppers

src/Xamarin.Android.Build.Tasks/Xamarin.Android.Common.targets

@@ -284,6 +284,7 @@ Copyright (C) 2011-2012 Xamarin. All rights reserved.
 	<AndroidDexGenerator   Condition=" '$(AndroidDexGenerator)' == '' ">dx</AndroidDexGenerator>
 	<!-- NOTE: $(AndroidLinkTool) would be blank if code shrinking is not used at all -->
 	<AndroidLinkTool       Condition=" '$(AndroidLinkTool)' == '' And '$(AndroidEnableProguard)' == 'True' ">proguard</AndroidLinkTool>
+	<AndroidEnableProguard Condition=" '$(AndroidLinkTool)' != '' ">True</AndroidEnableProguard>
 	<AndroidEnableDesugar  Condition=" '$(AndroidEnableDesugar)' == '' And ('$(AndroidDexGenerator)' == 'd8' Or '$(AndroidLinkTool)' == 'r8') ">True</AndroidEnableDesugar>
 	<AndroidEnableDesugar  Condition=" '$(AndroidEnableDesugar)' == '' ">False</AndroidEnableDesugar>
 

src/Xamarin.Android.Build.Tasks/Xamarin.Android.D8.targets

@@ -93,7 +93,7 @@ Copyright (C) 2018 Xamarin. All rights reserved.
     </CreateItem>
 
     <R8
-        Condition=" '$(AndroidLinkTool)' == 'r8' "
+        Condition=" '$(AndroidLinkTool)' == 'r8' and '$(_ProguardProjectConfiguration)' != '' "
         ToolPath="$(JavaToolPath)"
         JavaMaximumHeapSize="$(JavaMaximumHeapSize)"
         JavaOptions="$(JavaOptions)"

tests/Xamarin.Forms-Performance-Integration/Droid/Xamarin.Forms.Performance.Integration.Droid.csproj

@@ -136,6 +136,7 @@
     <None Include="Properties\AndroidManifest.xml" />
     <None Include="Resources\AboutResources.txt" />
     <None Include="packages.config" />
+    <ProguardConfiguration Include="proguard.cfg" />
   </ItemGroup>
   <ItemGroup>
     <Compile Include="Properties\AssemblyInfo.cs" />

tests/Xamarin.Forms-Performance-Integration/Droid/proguard.cfg

@@ -0,0 +1,2 @@
+-keep class android.support.v7.widget.** { *; }
+-dontwarn android.support.v7.widget.*