Cancel watching the mojo data pipe on download pause

When download is paused, watching the mojo data pipe for data ready
callback is not needed. As the callback will trigger an early return
and do nothing. We can register the callback later when download is
resumed.

BUG=927530

Change-Id: Ifc225241978cb34991846ffb4a6a40166e5fc953
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1748122Reviewed-by: David Trainor <dtrainor@chromium.org>
Commit-Queue: Min Qin <qinmin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#686590}

components/download/internal/common/download_file_impl.cc

@@ -555,6 +555,8 @@ void DownloadFileImpl::Pause() {
   DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
   is_paused_ = true;
   record_stream_bandwidth_ = false;
+  for (auto& stream : source_streams_)
+    stream.second->ClearDataReadyCallback();
 }
 
 void DownloadFileImpl::Resume() {
@@ -565,7 +567,7 @@ void DownloadFileImpl::Resume() {
   for (auto& stream : source_streams_) {
     SourceStream* source_stream = stream.second.get();
     if (!source_stream->is_finished()) {
-      StreamActive(source_stream, MOJO_RESULT_OK);
+      ActivateStream(source_stream);
     }
   }
 }
@@ -722,15 +724,19 @@ void DownloadFileImpl::RegisterAndActivateStream(SourceStream* source_stream) {
   DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
 
   source_stream->Initialize();
-  source_stream->RegisterDataReadyCallback(
-      base::Bind(&DownloadFileImpl::StreamActive, weak_factory_.GetWeakPtr(),
-                 source_stream));
   // Truncate |source_stream|'s length if necessary.
   for (const auto& received_slice : received_slices_) {
     source_stream->TruncateLengthWithWrittenDataBlock(
         received_slice.offset, received_slice.received_bytes);
   }
   num_active_streams_++;
+  ActivateStream(source_stream);
+}
+
+void DownloadFileImpl::ActivateStream(SourceStream* source_stream) {
+  source_stream->RegisterDataReadyCallback(
+      base::Bind(&DownloadFileImpl::StreamActive, weak_factory_.GetWeakPtr(),
+                 source_stream));
   StreamActive(source_stream, MOJO_RESULT_OK);
 }
 

components/download/public/common/download_file_impl.h

@@ -277,6 +277,9 @@ class COMPONENTS_DOWNLOAD_EXPORT DownloadFileImpl : public DownloadFile {
   // Register callback and start to read data from the stream.
   void RegisterAndActivateStream(SourceStream* source_stream);
 
+  // Helper method to activate a stream and start reading from it.
+  void ActivateStream(SourceStream* source_stream);
+
   // Called when a stream completes.
   void OnStreamCompleted(SourceStream* source_stream);