Recording download mime types for normal profile

content/browser/download/download_item_impl.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // File method ordering: Methods in this file are in the same order as
 // in download_item_impl.h, with the following exception: The public
 // interface Start is placed in chronological order with the other
 // (private) routines that together define a DownloadItem's state
 // transitions as the download progresses.  See "Download progression
 // cascade" later in this file.
@@ skipping 1240 matching lines @@
 
     // Otherwise, this was a resumption attempt which ended with an
     // interruption. Continue with current target path.
     TransitionTo(TARGET_RESOLVED_INTERNAL);
     InterruptWithPartialState(
         offset, std::move(hash_state), new_create_info.result);
     UpdateObservers();
     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_);
 
   if (state_ == RESUMING_INTERNAL)
     UpdateValidatorsOnResumption(new_create_info);
 
   TransitionTo(TARGET_PENDING_INTERNAL);
 
   job_->Start();
@@ skipping 894 matching lines @@
     case RESUME_MODE_USER_CONTINUE:
       return "USER_CONTINUE";
     case RESUME_MODE_USER_RESTART:
       return "USER_RESTART";
   }
   NOTREACHED() << "Unknown resume mode " << mode;
   return "unknown";
 }
 
 }  // namespace content