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 a16f585bc30ccd3af7630ca1d477d769d7f16bde..fcfa74aa636a8885f12f0c24ede7648618837a20 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.