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..71379a60061209e7c34341f835d7bd3c558864de 100644
--- a/content/browser/download/download_file_impl.cc
+++ b/content/browser/download/download_file_impl.cc
@@ -71,6 +71,9 @@ DownloadFileImpl::DownloadFileImpl(
       default_download_directory_(default_download_directory),
       is_sparse_file_(is_sparse_file),
       bytes_seen_(0),
+      num_active_streams_(0),
+      bytes_seen_with_parallel_streams_(0),
+      bytes_seen_without_parallel_streams_(0),
       received_slices_(received_slices),
       observer_(observer),
       weak_factory_(this) {
@@ -317,8 +320,18 @@ void DownloadFileImpl::StreamActive(SourceStream* source_stream) {
           reason = WriteDataToFile(
               source_stream->offset() + source_stream->bytes_written(),
               incoming_data.get()->data(), incoming_data_size);
-          disk_writes_time_ += (base::TimeTicks::Now() - write_start);
+          base::TimeDelta write_time = (base::TimeTicks::Now() - write_start);
+          disk_writes_time_ += write_time;
           bytes_seen_ += incoming_data_size;
+          if (is_sparse_file_) {
+            if (num_active_streams_ > 1) {
+              disk_writes_time_with_parallel_streams_ += write_time;
+              bytes_seen_with_parallel_streams_ += incoming_data_size;
+            } else {
+              disk_writes_time_without_parallel_streams_ += write_time;
+              bytes_seen_without_parallel_streams_ += incoming_data_size;
+            }
+          }
           total_incoming_data_size += incoming_data_size;
           if (reason == DOWNLOAD_INTERRUPT_REASON_NONE)
             source_stream->OnWriteBytesToDisk(incoming_data_size);
@@ -367,10 +380,12 @@ 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 +404,12 @@ 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_,
+                                    disk_writes_time_with_parallel_streams_,
+                                    bytes_seen_without_parallel_streams_,
+                                    disk_writes_time_without_parallel_streams_);
+      }
       weak_factory_.InvalidateWeakPtrs();
       std::unique_ptr<crypto::SecureHash> hash_state = file_.Finish();
       update_timer_.reset();
@@ -414,6 +435,7 @@ void DownloadFileImpl::RegisterAndActivateStream(SourceStream* source_stream) {
                                                weak_factory_.GetWeakPtr(),
                                                source_stream));
     StreamActive(source_stream);
+    num_active_streams_++;
   }
 }