Clear the received slices in DownloadItemImpl when etag changed.

content/browser/download/download_item_impl.cc

Index: content/browser/download/download_item_impl.cc
diff --git a/content/browser/download/download_item_impl.cc b/content/browser/download/download_item_impl.cc
index 5c2286bb11e6e38aafc0ea569ea1ea3040947b3a..68a29641a20793b79af074c1acb22be3ff6e333e 100644
--- a/content/browser/download/download_item_impl.cc
+++ b/content/browser/download/download_item_impl.cc
@@ -1028,8 +1028,10 @@ void DownloadItemImpl::UpdateValidatorsOnResumption(
   if (chain_iter != new_create_info.url_chain.end())
     origin_state |= ORIGIN_STATE_ON_RESUMPTION_ADDITIONAL_REDIRECTS;
   if (etag_ != new_create_info.etag ||
-      last_modified_time_ != new_create_info.last_modified)
+      last_modified_time_ != new_create_info.last_modified) {
+    received_slices_.clear();

[qinmin, 2017/04/07 18:03:49]

should we also clear the received_bytes_ after the
RecordOriginStateOnResumption().

The received_bytes_ will get cleared when DownloadFile updates its state through
a posted task. but if Chrome crashes before the update, then the etag_ and
last_modified_time_ has been updated to new values, but the received_bytes_
hasn't. If the db happens to commit the etag_ and last_modified_time_ change,
then if user restarts chrome and resumes the download, the download will not
start from offset 0.

[xingliu, 2017/04/07 20:50:08]

Done.

Make sense, it's good to clear received slices before the new
content_disposition is set in memory. So we have a lower chance to get
inconsistency in db records.

[xingliu, 2017/04/07 22:18:03]

Done,

Sorry that I somehow misunderstood the comment, set the received_bytes_ to 0
only when validators changed.

Also we probably shouldn't set the received_bytes_ to 0 after
RecordOriginStateOnResumption(), since when validators are not changed and
crashed before DownloadFile sets the received_bytes_, we probably should not
restart from 0.

     origin_state |= ORIGIN_STATE_ON_RESUMPTION_VALIDATORS_CHANGED;
+  }
   if (content_disposition_ != new_create_info.content_disposition)
     origin_state |= ORIGIN_STATE_ON_RESUMPTION_CONTENT_DISPOSITION_CHANGED;
   RecordOriginStateOnResumption(received_bytes_ != 0, origin_state);
@@ -1289,7 +1291,8 @@ void DownloadItemImpl::StartDownload() {
                  // Safe because we control download file lifetime.
                  base::Unretained(download_file_.get()),
                  base::Bind(&DownloadItemImpl::OnDownloadFileInitialized,
-                            weak_ptr_factory_.GetWeakPtr())));
+                            weak_ptr_factory_.GetWeakPtr()),
+                 received_slices_));
 }
 
 void DownloadItemImpl::OnDownloadFileInitialized(