Adding proguard flags

Bug: 3244266

Change-Id: I623325cb7224fe189db6abee92fe576c02468e98
diff --git a/proguard.flags b/proguard.flags
new file mode 100644
index 0000000..957cfa3
--- /dev/null
+++ b/proguard.flags
@@ -0,0 +1,8 @@
+-keep class com.android.providers.contacts.ContactsDatabaseHelper {
+  * <init>(...);
+}
+
+# Any methods whose name is '*ForTest' are preserved.
+-keep class ** {
+  *** *ForTest(...);
+}