Write XOR ops for bsdiff and puffdiff

Test: th
Bug: 177104308

Change-Id: I10f79f1a2de910e5ba57a72a5dba5901c9348d77
diff --git a/payload_generator/extent_ranges.h b/payload_generator/extent_ranges.h
index a16947e..08cf5fe 100644
--- a/payload_generator/extent_ranges.h
+++ b/payload_generator/extent_ranges.h
@@ -110,7 +110,7 @@
  private:
   ExtentSet extent_set_;
   uint64_t blocks_ = 0;
-  const bool merge_touching_extents_ = true;
+  bool merge_touching_extents_ = true;
 };
 
 // Filters out from the passed list of extents |extents| all the blocks in the