Fix NetworkFetcherWinHTTP memory leak.

The |write_data_callback_| holds a reference to the object, and the
object leaks due to the circular dependency.

TBR: waffles@chromium.org
Bug: 1088295
Change-Id: Ia897432681221abb07686be124a5e89409813095
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2224162Reviewed-by: Sorin Jianu <sorin@chromium.org>
Commit-Queue: Sorin Jianu <sorin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#773564}

chrome/updater/win/net/network_winhttp.cc

@@ -57,6 +57,9 @@ NetworkFetcherWinHTTP::NetworkFetcherWinHTTP(const HINTERNET& session_handle)
 NetworkFetcherWinHTTP::~NetworkFetcherWinHTTP() = default;
 
 void NetworkFetcherWinHTTP::Close() {
+  // |write_data_callback_| maintains an outstanding reference to this object
+  // and the reference must be released to avoid leaking the object.
+  write_data_callback_.Reset();
   request_handle_.reset();
 }