Add file group for java X25519 class

Test: manual test
Change-Id: I11f6b21db3c0bc1e1988822e834f9760d6636b90

Android.bp

diff --git a/Android.bp b/Android.bp
new file mode 100644
index 0000000..565a903
--- /dev/null
+++ b/Android.bp
@@ -0,0 +1,14 @@
+filegroup {
+    name: "tink-java-x25519-sources",
+    srcs: [
+        "java_src/src/main/java/com/google/crypto/tink/annotations/Alpha.java",
+        "java_src/src/main/java/com/google/crypto/tink/internal/Curve25519.java",
+        "java_src/src/main/java/com/google/crypto/tink/internal/Field25519.java",
+        "java_src/src/main/java/com/google/crypto/tink/internal/Random.java",
+        "java_src/src/main/java/com/google/crypto/tink/subtle/Bytes.java",
+        "java_src/src/main/java/com/google/crypto/tink/subtle/Hex.java",
+        "java_src/src/main/java/com/google/crypto/tink/subtle/Random.java",
+        "java_src/src/main/java/com/google/crypto/tink/subtle/X25519.java",
+    ],
+}
+