[Blobs] Fix BuildFromStreamResult histogram recording.

Only record in OnError if callback_ is still set. Otherwise every
success case will also result in recording "Aborted", via the destructor
of the class calling OnError.

Bug: 712693
Change-Id: I0d73119017b6d88fca4378687d5187ed96919b49
Reviewed-on: https://chromium-review.googlesource.com/994232
Commit-Queue: Daniel Murphy <dmurph@chromium.org>
Reviewed-by: Daniel Murphy <dmurph@chromium.org>
Cr-Commit-Position: refs/heads/master@{#548201}

storage/browser/blob/blob_builder_from_stream.cc

@@ -617,7 +617,6 @@ void BlobBuilderFromStream::DidWriteToExtendedFile(
 }
 
 void BlobBuilderFromStream::OnError(Result result) {
-  RecordResult(result);
   if (pending_quota_task_)
     pending_quota_task_->Cancel();
 
@@ -626,6 +625,7 @@ void BlobBuilderFromStream::OnError(Result result) {
 
   if (!callback_)
     return;
+  RecordResult(result);
   std::move(callback_).Run(this, nullptr);
 }