Binary compatibility tests for R8 API.

Change-Id: I0955b93bfd3d96aaaa2b5f5e95deb03573346d3f
diff --git a/build.gradle b/build.gradle
index 61a8943..c5fe273 100644
--- a/build.gradle
+++ b/build.gradle
@@ -715,6 +715,12 @@
     destinationDir file('tests')
 }
 
+task buildR8ApiUsageSample(type: Jar) {
+    from sourceSets.apiUsageSample.output
+    baseName 'r8_api_usage_sample'
+    destinationDir file('tests')
+}
+
 task buildDebugInfoExamplesDex {
     def examplesDir = file("src/test/java")
     def hostJar = "debuginfo_examples.jar"