Persist download interrupt reason, both target and current paths, and url_chain.

content/public/browser/download_interrupt_reason_values.h

Index: content/public/browser/download_interrupt_reason_values.h
diff --git a/content/public/browser/download_interrupt_reason_values.h b/content/public/browser/download_interrupt_reason_values.h
index 088052fa6e81163a28612ce2a8f012007db0e746..ab2cd90f9587e2ad1b6fceead1d096d35da1b028 100644
--- a/content/public/browser/download_interrupt_reason_values.h
+++ b/content/public/browser/download_interrupt_reason_values.h
@@ -2,6 +2,10 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// Note that the embedder is welcome to persist these values across
+// invocations of the browser, and possibly across browser versions.
+// Thus individual errors may be deprecated and new errors added, but
+// the values of particular errors should not be changed.
 
 // File errors.