Introduce ParallelDownloadJob.

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 47ad0ee6944fc98bafb52c0621adf81b0e10e239..b3649c822e07fb451a408e62478618603cae62ab 100644
--- a/content/browser/download/download_item_impl.cc
+++ b/content/browser/download/download_item_impl.cc
@@ -40,9 +40,11 @@
 #include "content/browser/download/download_file.h"
 #include "content/browser/download/download_interrupt_reasons_impl.h"
 #include "content/browser/download/download_item_impl_delegate.h"
+#include "content/browser/download/download_job_factory.h"
 #include "content/browser/download/download_net_log_parameters.h"
 #include "content/browser/download/download_request_handle.h"
 #include "content/browser/download/download_stats.h"
+#include "content/browser/download/download_url_job.h"
 #include "content/browser/renderer_host/render_view_host_impl.h"
 #include "content/browser/web_contents/web_contents_impl.h"
 #include "content/public/browser/browser_context.h"
@@ -237,7 +239,6 @@ DownloadItemImpl::DownloadItemImpl(
     std::unique_ptr<DownloadRequestHandleInterface> request_handle,
     const net::NetLogWithSource& net_log)
     : is_save_package_download_(true),
-      request_handle_(std::move(request_handle)),
       guid_(base::ToUpperASCII(base::GenerateGUID())),
       download_id_(download_id),
       target_path_(path),
@@ -251,6 +252,9 @@ DownloadItemImpl::DownloadItemImpl(
       current_path_(path),
       net_log_(net_log),
       weak_ptr_factory_(this) {
+  job_ = base::MakeUnique<DownloadUrlJob>(std::move(request_handle));
+  job_->Attach(this);
+
   delegate_->Attach();
   Init(true /* actively downloading */, SRC_SAVE_PAGE_AS);
 }
@@ -367,7 +371,7 @@ void DownloadItemImpl::Pause() {
 
     case IN_PROGRESS_INTERNAL:
     case TARGET_PENDING_INTERNAL:
-      request_handle_->PauseRequest();
+      job_->Pause();
       is_paused_ = true;

[asanka, 2017/02/16 16:27:39]

Consider removing is_paused_ and having the job_ keep track of the paused state.

[xingliu, 2017/02/20 18:59:10]

Done. Makes sense.

       UpdateObservers();
       return;
@@ -394,7 +398,7 @@ void DownloadItemImpl::Resume() {
     case IN_PROGRESS_INTERNAL:
       if (!is_paused_)
         return;
-      request_handle_->ResumeRequest();
+      job_->Resume();
       is_paused_ = false;
       UpdateObservers();
       return;
@@ -772,9 +776,9 @@ WebContents* DownloadItemImpl::GetWebContents() const {
   // paths that might be used by DownloadItems created from history import.
   // Currently such items have null request_handle_s, where other items
   // (regular and SavePackage downloads) have actual objects off the pointer.
-  if (request_handle_)
-    return request_handle_->GetWebContents();
-  return NULL;
+  if (job_)
+    return job_->GetWebContents();
+  return nullptr;
 }
 
 void DownloadItemImpl::OnContentCheckCompleted(DownloadDangerType danger_type) {
@@ -1172,15 +1176,14 @@ void DownloadItemImpl::Start(
   DVLOG(20) << __func__ << "() this=" << DebugString(true);
 
   download_file_ = std::move(file);
-  request_handle_ = std::move(req_handle);
+  job_ = DownloadJobFactory::CreateJob(std::move(req_handle), new_create_info);
   destination_error_ = DOWNLOAD_INTERRUPT_REASON_NONE;
 
   if (state_ == CANCELLED_INTERNAL) {
     // The download was in the process of resuming when it was cancelled. Don't
     // proceed.
     ReleaseDownloadFile(true);
-    if (request_handle_)
-      request_handle_->CancelRequest();
+    job_->Cancel(true);
     return;
   }
 
@@ -1232,13 +1235,18 @@ void DownloadItemImpl::Start(
 
   // Successful download start.
   DCHECK(download_file_.get());
-  DCHECK(request_handle_.get());
+  DCHECK(job_.get());
 
   if (state_ == RESUMING_INTERNAL)
     UpdateValidatorsOnResumption(new_create_info);
 
   TransitionTo(TARGET_PENDING_INTERNAL);
 
+  job_->Attach(this);

[asanka, 2017/02/16 16:27:39]

Why is there a separate Attach() method?

It would be reasonable to assume that the job would be bound to the same
DownloadItemImpl for its entire lifetime, and that DownloadItemImpl will outlive
the job. This implies that we would be able associate a Job with a
DownloadItemImpl at creation and leave it at that.

[xingliu, 2017/02/20 18:59:10]

Done. Move to pass the item in ctor.

+  job_->Start();
+}
+
+void DownloadItemImpl::InitializeDownloadFile() {

[asanka, 2017/02/16 16:27:39]

This isn't so much initializing the download file, but setting in motion the
entire series of events that result in the file being downloaded.

[xingliu, 2017/02/20 18:59:10]

Done, renamed to StartDownloadProgress.

   BrowserThread::PostTask(
       BrowserThread::FILE, FROM_HERE,
       base::Bind(&DownloadFile::Initialize,
@@ -1635,8 +1643,8 @@ void DownloadItemImpl::InterruptWithPartialState(
     SetHashState(std::move(hash_state));
   }
 
-  if (request_handle_)
-    request_handle_->CancelRequest();
+  if (job_.get())
+    job_->Cancel(false);
 
   if (reason == DOWNLOAD_INTERRUPT_REASON_USER_CANCELED ||
       reason == DOWNLOAD_INTERRUPT_REASON_USER_SHUTDOWN) {
@@ -1776,7 +1784,7 @@ void DownloadItemImpl::TransitionTo(DownloadInternalState new_state) {
       DCHECK(current_path_.DirName() == target_path_.DirName())
           << "Current output directory must match target directory.";
       DCHECK(download_file_) << "Output file must be owned by download item.";
-      DCHECK(request_handle_) << "Download source must be active.";
+      DCHECK(job_) << "Must have active download job.";
       DCHECK(!is_paused_) << "At the time a download enters IN_PROGRESS state, "
                              "it must not be paused.";
       break;