Merge "Add default proguard flags from guava"

# See bug/20658265.

# -dontwarn android.support.**

# From https://github.com/google/guava/wiki/UsingProGuardWithGuava

# Striped64, LittleEndianByteArray, UnsignedBytes, AbstractFuture

-dontwarn sun.misc.Unsafe

# Futures.getChecked (which often won't work with Proguard anyway) uses this. It

# has a fallback, but again, don't use Futures.getChecked on Android regardless.

-dontwarn java.lang.ClassValue

# Less spammy.

-dontnote