Recording download mime types for normal profile

content/browser/download/download_item_impl.cc

Index: content/browser/download/download_item_impl.cc
diff --git a/content/browser/download/download_item_impl.cc b/content/browser/download/download_item_impl.cc
index f118a476be598052f23acd1ffe392e303b084e39..bbbe7849c218d64c7ec6c2febce17e715268cd4b 100644
--- a/content/browser/download/download_item_impl.cc
+++ b/content/browser/download/download_item_impl.cc
@@ -1258,6 +1258,12 @@ void DownloadItemImpl::Start(
     return;
   }
 
+  RecordDownloadMimeType(mime_type_);

[shaktisahu, 2017/03/16 23:39:49]

asanka@ - I moved this from DownloadRequestCore::OnResponseStarted as I don't
have access to IsOffTheRecord() over there. I can move this to the beginning of
the function also. However I think, compared to the older location, I am missing
two return points inside DownloadResourceHandler::OnStart and 
DownloadManagerImpl::StartDownloadWithId. Will that cause significant change in
the metrics behavior?
Other option would be add a completely new metrics such as
Download.Start.ContentType and its counterpart for this purpose.

[asanka, 2017/03/17 15:19:27]

This is fine. The early return at DownloadResourceHandler::OnStart() is only
taken if the result is a cancellation. The original location wouldn't have
recorded UMA for that case anyway.

The only discrepancy is the one where the server response indicates a success,
but DownloadManagerImpl throws the response away before we get here because the
download was cancelled between issuing the request and receiving the response.
The incidence rate of that should be within noise.

Also, that case would only happen for resumption. I'll address the implications
of this as a top level comment.

+  if (GetWebContents() &&
+      !GetWebContents()->GetBrowserContext()->IsOffTheRecord()) {
+    RecordDownloadMimeTypeForNormalProfile(mime_type_);
+  }
+
   // Successful download start.
   DCHECK(download_file_);
   DCHECK(job_);