Use -keepparameternames for the r8lib build

Fixed: 174732681
Change-Id: I28a7c036afd0468ad75940abab285fa99d8f03ea
diff --git a/src/main/keep.txt b/src/main/keep.txt
index f8bbc12..82f6965 100644
--- a/src/main/keep.txt
+++ b/src/main/keep.txt
@@ -20,6 +20,7 @@
 
 -keepattributes SourceFile, LineNumberTable, InnerClasses, EnclosingMethod, Exceptions, Signature
 
+-keepparameternames
 -keeppackagenames com.android.tools.r8
 -repackageclasses com.android.tools.r8.internal