Fix LatinIME's ProGuard config for support libs using flags copied from Email app.

Bug: 5829051
Change-Id: Ie1784d1ba1a4515ab492a06d7adc10c7d54a64c5
diff --git a/java/proguard.flags b/java/proguard.flags
index 5ce0c27..a5a6679 100644
--- a/java/proguard.flags
+++ b/java/proguard.flags
@@ -38,3 +38,9 @@
 -keep class com.android.inputmethod.keyboard.MoreKeysKeyboard$Builder$MoreKeysKeyboardParams {
   <init>(...);
 }
+
+# The support library contains references to newer platform versions.
+# Don't warn about those in case this app is linking against an older
+# platform version.  We know about them, and they are safe.
+-dontwarn android.support.v4.**
+-dontwarn android.support.v13.**