Add UMA for estimating disk bandwidth and the time saved with parallel download

content/browser/download/download_file_impl.cc

Index: content/browser/download/download_file_impl.cc
diff --git a/content/browser/download/download_file_impl.cc b/content/browser/download/download_file_impl.cc
index e4ec806f7718c8b4de357eb9977f329a852834a7..3530c649666ce90eeb68f19ee80be6cff09626fa 100644
--- a/content/browser/download/download_file_impl.cc
+++ b/content/browser/download/download_file_impl.cc
@@ -71,6 +71,10 @@ DownloadFileImpl::DownloadFileImpl(
       default_download_directory_(default_download_directory),
       is_sparse_file_(is_sparse_file),
       bytes_seen_(0),
+      num_active_streams_(0),
+      record_stream_bandwidth_(true),
+      bytes_seen_with_parallel_streams_(0),
+      bytes_seen_without_parallel_streams_(0),
       received_slices_(received_slices),
       observer_(observer),
       weak_factory_(this) {
@@ -116,6 +120,7 @@ void DownloadFileImpl::Initialize(const InitializeCallback& callback) {
   }
 
   download_start_ = base::TimeTicks::Now();
+  last_update_time_ = download_start_;
 
   // Primarily to make reset to zero in restart visible to owner.
   SendUpdate();
@@ -279,6 +284,10 @@ bool DownloadFileImpl::InProgress() const {
   return file_.in_progress();
 }
 
+void DownloadFileImpl::Pause() {
+  record_stream_bandwidth_ = false;

[xingliu, 2017/03/17 00:02:15]

I think we didn't set it to true again, and didn't use this in the file.

If set it to true again, maybe a Resume call? and maybe guard the bandwidth
metric logic with if (record_stream_bandwidth_).


If we discard the bandwidth metric after a pause, I think that's fine too, so we
only record contiguous download. But still need to if (record_stream_bandwidth_)
somewhere.

[David Trainor- moved to gerrit, 2017/03/17 07:25:40]

Do we need to reset last_update_time_ on resume as well?

[qinmin, 2017/03/17 19:52:54]

We don't record UMA even if resume is called, the value will contain too many
noises and could go very inaccurate.

[qinmin, 2017/03/17 19:52:55]

we should stop recording if a download is ever paused.
The variable is now used in the logic to determine if we should record the
download stats.

+}
+
 void DownloadFileImpl::StreamActive(SourceStream* source_stream) {
   DCHECK(source_stream->stream_reader());
   base::TimeTicks start(base::TimeTicks::Now());
@@ -367,10 +376,12 @@ void DownloadFileImpl::StreamActive(SourceStream* source_stream) {
         BrowserThread::UI, FROM_HERE,
         base::Bind(&DownloadDestinationObserver::DestinationError, observer_,
                    reason, TotalBytesReceived(), base::Passed(&hash_state)));
+    num_active_streams_--;
   } else if (state == ByteStreamReader::STREAM_COMPLETE || should_terminate) {
     // Signal successful completion or termination of the current stream.
     source_stream->stream_reader()->RegisterCallback(base::Closure());
     source_stream->set_finished(true);
+    num_active_streams_--;
 
     // Inform observers.
     SendUpdate();
@@ -389,6 +400,12 @@ void DownloadFileImpl::StreamActive(SourceStream* source_stream) {
     if (all_stream_complete) {
       RecordFileBandwidth(bytes_seen_, disk_writes_time_,
                           base::TimeTicks::Now() - download_start_);
+      if (is_sparse_file_) {
+        RecordParallelDownloadStats(bytes_seen_with_parallel_streams_,
+                                    download_time_with_parallel_streams_,
+                                    bytes_seen_without_parallel_streams_,
+                                    download_time_without_parallel_streams_);
+      }
       weak_factory_.InvalidateWeakPtrs();
       std::unique_ptr<crypto::SecureHash> hash_state = file_.Finish();
       update_timer_.reset();
@@ -414,6 +431,7 @@ void DownloadFileImpl::RegisterAndActivateStream(SourceStream* source_stream) {
                                                weak_factory_.GetWeakPtr(),
                                                source_stream));
     StreamActive(source_stream);
+    num_active_streams_++;
   }
 }
 
@@ -438,6 +456,18 @@ void DownloadFileImpl::WillWriteToDisk(size_t data_len) {
                          this, &DownloadFileImpl::SendUpdate);
   }
   rate_estimator_.Increment(data_len);
+  if (is_sparse_file_) {
+    base::TimeTicks now = base::TimeTicks::Now();
+    base::TimeDelta time_elapsed = (now - last_update_time_);
+    last_update_time_ = now;
+    if (num_active_streams_ > 1) {
+      download_time_with_parallel_streams_ += time_elapsed;
+      bytes_seen_with_parallel_streams_ += data_len;
+    } else {
+      download_time_without_parallel_streams_ += time_elapsed;
+      bytes_seen_without_parallel_streams_ += data_len;
+    }
+  }
 }
 
 DownloadFileImpl::RenameParameters::RenameParameters(