Expose enableSameFilePolicy via system property.

This will let chrome remove a custom patch.

Change-Id: I78f9087c3b1efa02b927e4202ba3b16a14d06d1a
diff --git a/src/main/java/com/android/tools/r8/utils/InternalOptions.java b/src/main/java/com/android/tools/r8/utils/InternalOptions.java
index 9af4f06..e653a7a 100644
--- a/src/main/java/com/android/tools/r8/utils/InternalOptions.java
+++ b/src/main/java/com/android/tools/r8/utils/InternalOptions.java
@@ -1548,7 +1548,8 @@
     private boolean enableInterfaceMerging =
         System.getProperty("com.android.tools.r8.enableHorizontalInterfaceMerging") != null;
     private boolean enableInterfaceMergingInInitial = false;
-    private boolean enableSameFilePolicy = false;
+    private boolean enableSameFilePolicy =
+        System.getProperty("com.android.tools.r8.enableSameFilePolicy") != null;
     private boolean enableSyntheticMerging = true;
     private boolean ignoreRuntimeTypeChecksForTesting = false;
     private boolean restrictToSynthetics = false;