NativeDesktopMediaList: do desktop capture on an exclusive thread

webrtc::ScreenCapturerMac requires to be started and destroyed on same
thread. The current SequencedTaskRunner can't satisfy this and will
cause random crashes.
This cl is to use an exclusive capture thread as same as the one in
content/browser/media/capture/desktop_capture_device.cc.

Bug: 877982,851883
Change-Id: I6508add3660f63e1d2539dd2175a131f869a836a
Reviewed-on: https://chromium-review.googlesource.com/1199806
Commit-Queue: Weiyong Yao <braveyao@chromium.org>
Reviewed-by: Julien Isorce <julien.isorce@chromium.org>
Cr-Commit-Position: refs/heads/master@{#588151}

chrome/browser/media/webrtc/native_desktop_media_list.cc

@@ -5,8 +5,11 @@
 #include "chrome/browser/media/webrtc/native_desktop_media_list.h"
 
 #include "base/hash.h"
+#include "base/single_thread_task_runner.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/task/post_task.h"
+#include "base/threading/thread_restrictions.h"
+#include "build/build_config.h"
 #include "chrome/browser/media/webrtc/desktop_media_list_observer.h"
 #include "chrome/grit/generated_resources.h"
 #include "content/public/browser/browser_thread.h"
@@ -76,11 +79,13 @@ gfx::ImageSkia ScaleDesktopFrame(std::unique_ptr<webrtc::DesktopFrame> frame,
 class NativeDesktopMediaList::Worker
     : public webrtc::DesktopCapturer::Callback {
  public:
-  Worker(base::WeakPtr<NativeDesktopMediaList> media_list,
+  Worker(scoped_refptr<base::SingleThreadTaskRunner> task_runner,
+         base::WeakPtr<NativeDesktopMediaList> media_list,
          DesktopMediaID::Type type,
          std::unique_ptr<webrtc::DesktopCapturer> capturer);
   ~Worker() override;
 
+  void Start();
   void Refresh(const DesktopMediaID::Id& view_dialog_id);
 
   void RefreshThumbnails(const std::vector<DesktopMediaID>& native_ids,
@@ -93,6 +98,9 @@ class NativeDesktopMediaList::Worker
   void OnCaptureResult(webrtc::DesktopCapturer::Result result,
                        std::unique_ptr<webrtc::DesktopFrame> frame) override;
 
+  // Task runner used for capturing operations.
+  scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
+
   base::WeakPtr<NativeDesktopMediaList> media_list_;
 
   DesktopMediaID::Type type_;
@@ -106,17 +114,27 @@ class NativeDesktopMediaList::Worker
 };
 
 NativeDesktopMediaList::Worker::Worker(
+    scoped_refptr<base::SingleThreadTaskRunner> task_runner,
     base::WeakPtr<NativeDesktopMediaList> media_list,
     DesktopMediaID::Type type,
     std::unique_ptr<webrtc::DesktopCapturer> capturer)
-    : media_list_(media_list), type_(type), capturer_(std::move(capturer)) {
-  capturer_->Start(this);
+    : task_runner_(task_runner),
+      media_list_(media_list),
+      type_(type),
+      capturer_(std::move(capturer)) {}
+
+NativeDesktopMediaList::Worker::~Worker() {
+  DCHECK(task_runner_->BelongsToCurrentThread());
 }
 
-NativeDesktopMediaList::Worker::~Worker() {}
+void NativeDesktopMediaList::Worker::Start() {
+  DCHECK(task_runner_->BelongsToCurrentThread());
+  capturer_->Start(this);
+}
 
 void NativeDesktopMediaList::Worker::Refresh(
     const DesktopMediaID::Id& view_dialog_id) {
+  DCHECK(task_runner_->BelongsToCurrentThread());
   std::vector<SourceDescription> result;
 
   webrtc::DesktopCapturer::SourceList sources;
@@ -163,6 +181,7 @@ void NativeDesktopMediaList::Worker::Refresh(
 void NativeDesktopMediaList::Worker::RefreshThumbnails(
     const std::vector<DesktopMediaID>& native_ids,
     const gfx::Size& thumbnail_size) {
+  DCHECK(task_runner_->BelongsToCurrentThread());
   ImageHashesMap new_image_hashes;
 
   // Get a thumbnail for each native source.
@@ -210,17 +229,30 @@ NativeDesktopMediaList::NativeDesktopMediaList(
     std::unique_ptr<webrtc::DesktopCapturer> capturer)
     : DesktopMediaListBase(base::TimeDelta::FromMilliseconds(
           kDefaultNativeDesktopMediaListUpdatePeriod)),
+      thread_("DesktopMediaListCaptureThread"),
       weak_factory_(this) {
   type_ = type;
-  capture_task_runner_ = base::CreateSequencedTaskRunnerWithTraits(
-      {base::MayBlock(), base::TaskPriority::USER_VISIBLE});
 
-  worker_.reset(
-      new Worker(weak_factory_.GetWeakPtr(), type, std::move(capturer)));
+#if defined(OS_WIN) || defined(OS_MACOSX)
+  // On Windows/OSX the thread must be a UI thread.
+  base::MessageLoop::Type thread_type = base::MessageLoop::TYPE_UI;
+#else
+  base::MessageLoop::Type thread_type = base::MessageLoop::TYPE_DEFAULT;
+#endif
+  thread_.StartWithOptions(base::Thread::Options(thread_type, 0));
+
+  worker_.reset(new Worker(thread_.task_runner(), weak_factory_.GetWeakPtr(),
+                           type, std::move(capturer)));
+
+  thread_.task_runner()->PostTask(
+      FROM_HERE,
+      base::BindOnce(&Worker::Start, base::Unretained(worker_.get())));
 }
 
 NativeDesktopMediaList::~NativeDesktopMediaList() {
-  capture_task_runner_->DeleteSoon(FROM_HERE, worker_.release());
+  base::ThreadRestrictions::ScopedAllowIO allow_io;
+  thread_.task_runner()->DeleteSoon(FROM_HERE, worker_.release());
+  thread_.Stop();
 }
 
 void NativeDesktopMediaList::Refresh() {
@@ -230,7 +262,7 @@ void NativeDesktopMediaList::Refresh() {
   new_aura_thumbnail_hashes_.clear();
 #endif
 
-  capture_task_runner_->PostTask(
+  thread_.task_runner()->PostTask(
       FROM_HERE,
       base::BindOnce(&Worker::Refresh, base::Unretained(worker_.get()),
                      view_dialog_id_.id));
@@ -280,7 +312,7 @@ void NativeDesktopMediaList::RefreshForAuraWindows(
 #if defined(USE_AURA)
     pending_native_thumbnail_capture_ = true;
 #endif
-    capture_task_runner_->PostTask(
+    thread_.task_runner()->PostTask(
         FROM_HERE, base::BindOnce(&Worker::RefreshThumbnails,
                                   base::Unretained(worker_.get()), native_ids,
                                   thumbnail_size_));

chrome/browser/media/webrtc/native_desktop_media_list.h

@@ -8,7 +8,7 @@
 #include <memory>
 
 #include "base/memory/weak_ptr.h"
-#include "base/sequenced_task_runner.h"
+#include "base/threading/thread.h"
 #include "chrome/browser/media/webrtc/desktop_media_list_base.h"
 #include "content/public/browser/desktop_media_id.h"
 #include "ui/gfx/image/image.h"
@@ -44,12 +44,7 @@ class NativeDesktopMediaList : public DesktopMediaListBase {
                                gfx::Image image);
 #endif
 
-  // Task runner used for the |worker_|.
-  scoped_refptr<base::SequencedTaskRunner> capture_task_runner_;
-
-  // An object that does all the work of getting list of sources on a background
-  // thread (see |capture_task_runner_|). Destroyed on |capture_task_runner_|
-  // after the model is destroyed.
+  base::Thread thread_;
   std::unique_ptr<Worker> worker_;
 
 #if defined(USE_AURA)