Always resume download for CONTENT_LENGTH_MISMATCH errors

When strong validators are not present, we don't resume download if
CONTENT_LENGTH_MISMATCH error happens.
However, according to UMA, more than 99% of the cases more data will
be received after a CONTENT_LENGTH_MISMATCH error if strong validators
are present. And since we are launching the feature to allow download
resumption without strong validators, many of these interrupted
downloads can now resume.

BUG=1002591

Change-Id: I75facafef994e6c4637e52b340dddc05fca94833
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1795761Reviewed-by: Xing Liu <xingliu@chromium.org>
Reviewed-by: David Trainor <dtrainor@chromium.org>
Commit-Queue: Min Qin <qinmin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#695375}

components/download/internal/common/download_utils.cc

@@ -57,23 +57,6 @@ DownloadInterruptReason HandleRequestCompletionStatus(
     net::CertStatus cert_status,
     bool is_partial_request,
     DownloadInterruptReason abort_reason) {
-  // ERR_CONTENT_LENGTH_MISMATCH can be caused by 1 of the following reasons:
-  // 1. Server or proxy closes the connection too early.
-  // 2. The content-length header is wrong.
-  // If the download has strong validators, we can interrupt the download
-  // and let it resume automatically. Otherwise, resuming the download will
-  // cause it to restart and the download may never complete if the error was
-  // caused by reason 2. As a result, downloads without strong validators are
-  // treated as completed here.
-  // TODO(qinmin): check the metrics from downloads with strong validators,
-  // and decide whether we should interrupt downloads without strong validators
-  // rather than complete them.
-  if (error_code == net::ERR_CONTENT_LENGTH_MISMATCH &&
-      !has_strong_validators) {
-    error_code = net::OK;
-    RecordDownloadCount(COMPLETED_WITH_CONTENT_LENGTH_MISMATCH_COUNT);
-  }
-
   if (error_code == net::ERR_ABORTED) {
     // ERR_ABORTED == something outside of the network
     // stack cancelled the request.  There aren't that many things that