Update to protobuf 3.10 lite.

java/build.gradle

@@ -1,4 +1,16 @@
+buildscript {
+    repositories {
+        google()
+        mavenCentral()
+    }
+
+    dependencies {
+        classpath 'com.google.protobuf:protobuf-gradle-plugin:0.8.10'
+    }
+}
+
 apply plugin: 'java'
+apply plugin: 'com.google.protobuf'
 apply plugin: 'maven'
 apply plugin: 'signing'
 
@@ -22,10 +34,29 @@ sourceSets {
 
 dependencies {
     compile "org.whispersystems:signal-protocol-java:${protocol_version}"
+    compile 'com.google.protobuf:protobuf-javalite:3.10.0'
 
     testCompile ('junit:junit:3.8.2')
 }
 
+protobuf {
+    protoc {
+        artifact = 'com.google.protobuf:protoc:3.10.0'
+    }
+    generateProtoTasks {
+        all().each { task ->
+            task.builtins {
+                java {
+                    option "lite"
+                }
+            }
+        }
+    }
+}
+
+sourceSets {
+    main.proto.srcDir '../protobuf'
+}
 
 test {
     testLogging {

protobuf/Makefile

@@ -1,3 +0,0 @@
-
-all:
-	protoc --java_out=../java/src/main/java/ UnidentifiedDelivery.proto

protobuf/UnidentifiedDelivery.proto

@@ -1,6 +1,8 @@
+syntax = "proto2";
+
 package signal;
 
-option java_package = "org.signal.libsignal.metadata";
+option java_package         = "org.signal.libsignal.metadata";
 option java_outer_classname = "SignalProtos";
 
 message ServerCertificate {