Class.forName(String) is understood by ProGuard, removing the need for
manual ProGuard configuration and allows ProGuard to rename the provider
classes. Previously the provider classes could not be renamed.
Fixes#2633
Fixes#2207. This is actually a workaround. Ideally users shouldn't need
to -keep classes, but it's a bit risky to fix the real issue before 1.1.
The further fix will be done as part of #2633.
The interop app's build.gradle change is necessary to compile with newer
Gradle versions. The com.google.errorprone.annotations was necessary in
order to prevent annotation warnings from failing the build.
Eric Anderson
Xiao Hang