Mojo: Reject writes when ChannelWin IO fails

This is marginally better than what we're doing now, but more
importantly it satisfies a reasonable DCHECK that we currently
violate in these cases.

Bug: 829290
Change-Id: I68621d4f1c8f40c1b689d74e801c1cdb77e4663a
Reviewed-on: https://chromium-review.googlesource.com/997769Reviewed-by: Wez <wez@chromium.org>
Commit-Queue: Ken Rockot <rockot@chromium.org>
Cr-Commit-Position: refs/heads/master@{#548463}

mojo/edk/system/channel_win.cc

@@ -175,10 +175,15 @@ class ChannelWin : public Channel,
                      DWORD bytes_transfered,
                      DWORD error) override {
     if (error != ERROR_SUCCESS) {
-      if (context == &write_context_)
+      if (context == &write_context_) {
+        {
+          base::AutoLock lock(write_lock_);
+          reject_writes_ = true;
+        }
         OnWriteError(Error::kDisconnected);
-      else
+      } else {
         OnError(Error::kDisconnected);
+      }
     } else if (context == &connect_context_) {
       DCHECK(is_connect_pending_);
       is_connect_pending_ = false;