Keep setAnimatedHeight pls

Or animating leavebehinditems doesn't work

Change-Id: I0f5f92aad2a711bcd273d1d3aa0e34f2d405e5b1
diff --git a/proguard.flags b/proguard.flags
index b014d70..6bc0847 100644
--- a/proguard.flags
+++ b/proguard.flags
@@ -44,6 +44,10 @@
   *** setAnimatedHeight(...);
 }
 
+-keepclasseswithmembers class com.android.mail.ui.LeaveBehindItem {
+  *** setAnimatedHeight(...);
+}
+
 -keepclasseswithmembers class com.android.mail.ui.ConversationViewFragment$MailJsBridge {
   public <methods>;
 }