update_engine: replace std::vector<char> with chromeos::Blob

To make update engine consistent with the rest of platform2 code
replaced std::vector<char> as the container of binary data with
chromeos::Blob.

BUG=None
TEST=`FEATURES=test emerge-link update_engine`

Change-Id: I6385fd2257d15aa24bfa74ac35512c2a06c33012
Reviewed-on: https://chromium-review.googlesource.com/247793
Reviewed-by: Gilad Arnold <garnold@chromium.org>
Reviewed-by: Alex Deymo <deymo@chromium.org>
Tested-by: Alex Vakulenko <avakulenko@chromium.org>
Commit-Queue: Alex Vakulenko <avakulenko@chromium.org>
diff --git a/multi_range_http_fetcher.cc b/multi_range_http_fetcher.cc
index 63b85c9..07118a3 100644
--- a/multi_range_http_fetcher.cc
+++ b/multi_range_http_fetcher.cc
@@ -74,8 +74,8 @@
 
 // State change: Downloading -> Downloading or Pending transfer ended
 void MultiRangeHttpFetcher::ReceivedBytes(HttpFetcher* fetcher,
-                                          const char* bytes,
-                                          int length) {
+                                          const void* bytes,
+                                          size_t length) {
   CHECK_LT(current_index_, ranges_.size());
   CHECK_EQ(fetcher, base_fetcher_.get());
   CHECK(!pending_transfer_ended_);