Only use DexItemBasedConstString in proto shrinker when minification is enabled

Change-Id: I4173ad7914b84c29b15f3d506f1d748b366c4b50
diff --git a/src/main/java/com/android/tools/r8/ir/analysis/proto/schema/ProtoFieldObject.java b/src/main/java/com/android/tools/r8/ir/analysis/proto/schema/ProtoFieldObject.java
index c3f7795..809791f 100644
--- a/src/main/java/com/android/tools/r8/ir/analysis/proto/schema/ProtoFieldObject.java
+++ b/src/main/java/com/android/tools/r8/ir/analysis/proto/schema/ProtoFieldObject.java
@@ -9,6 +9,7 @@
 import com.android.tools.r8.ir.analysis.type.Nullability;
 import com.android.tools.r8.ir.analysis.type.TypeLatticeElement;
 import com.android.tools.r8.ir.code.BasicBlock.ThrowingInfo;
+import com.android.tools.r8.ir.code.ConstString;
 import com.android.tools.r8.ir.code.DexItemBasedConstString;
 import com.android.tools.r8.ir.code.IRCode;
 import com.android.tools.r8.ir.code.Instruction;
@@ -28,10 +29,11 @@
     Value value =
         code.createValue(
             TypeLatticeElement.stringClassType(appView, Nullability.definitelyNotNull()));
-    return new DexItemBasedConstString(
-        value,
-        field,
-        FieldNameComputationInfo.forFieldName(),
-        ThrowingInfo.defaultForConstString(appView.options()));
+    ThrowingInfo throwingInfo = ThrowingInfo.defaultForConstString(appView.options());
+    if (appView.options().isMinifying()) {
+      return new DexItemBasedConstString(
+          value, field, FieldNameComputationInfo.forFieldName(), throwingInfo);
+    }
+    return new ConstString(value, field.name, throwingInfo);
   }
 }