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.
This improves our documentation for the gradle protobuf plugin, as its
version is dependent on the gradle version.
Gradle now has the --tests flag, performance improvements, and support
for OpenPGP subkeys.
com.android.tools.build:gradle:1.1.0 doesn't work with Gradle 2.10, but
1.5.0 does.
I also bumped the protobuf-gradle-plugin to be the same as the version
used in the README and our primary build.gradle.
Eric Anderson
Kun Zhang
Louis Ryan
Xudong Ma