Tab Capture: Backing store readbacks to YV12 VideoFrames.

content/browser/renderer_host/media/web_contents_video_capture_device.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
 // Implementation notes: This needs to work on a variety of hardware
 // configurations where the speed of the CPU and GPU greatly affect overall
 // performance.  Therefore, the process of capturing has been split up into a
 // pipeline of three stages.  Each stage executes on its own thread:
 //
 //   1. Capture: A bitmap is snapshotted/copied from the RenderView's backing
@@ skipping 46 matching lines @@
 #include "base/time.h"
 #include "content/browser/renderer_host/media/web_contents_capture_util.h"
 #include "content/browser/web_contents/web_contents_impl.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/render_process_host.h"
 #include "content/public/browser/render_view_host.h"
 #include "content/public/browser/render_widget_host_view.h"
 #include "content/public/browser/web_contents.h"
 #include "content/public/browser/web_contents_observer.h"
 #include "media/base/bind_to_loop.h"
+#include "media/base/video_frame.h"
 #include "media/video/capture/video_capture_types.h"
 #include "skia/ext/image_operations.h"
 #include "third_party/skia/include/core/SkBitmap.h"
 #include "third_party/skia/include/core/SkColor.h"
 #include "ui/gfx/rect.h"
+#include "ui/gfx/skia_util.h"
 
 // Used to self-trampoline invocation of methods to the approprate thread.  This
 // should be used sparingly, only when it's not clear which thread is invoking a
 // method.
 #define ENSURE_INVOKED_ON_THREAD(thread, ...) {  \
   DCHECK(thread.IsRunning());  \
   if (MessageLoop::current() != thread.message_loop()) {  \
     thread.message_loop()->PostTask(FROM_HERE, base::Bind(__VA_ARGS__));  \
     return;  \
   }  \
@@ skipping 50 matching lines @@
   fitted_width = std::max(kMinFrameWidth, MakeEven(fitted_width));
   fitted_height = std::max(kMinFrameHeight, MakeEven(fitted_height));
 
   *fitted_size = gfx::Size(fitted_width, fitted_height);
 }
 
 // Keeps track of the RenderView to be sourced, and executes copying of the
 // backing store on the UI BrowserThread.
 class BackingStoreCopier : public WebContentsObserver {
  public:
-  // Result status and done callback used with StartCopy().
-  enum Result {
-    OK,
-    TRANSIENT_ERROR,
-    NO_SOURCE,
-  };
-  typedef base::Callback<void(Result result,
-                              const SkBitmap& capture,
-                              const base::Time& capture_time)> DoneCB;
-
   BackingStoreCopier(int render_process_id, int render_view_id);
 
   // If non-NULL, use the given |override| to access the backing store.
   // This is used for unit testing.
   void SetRenderWidgetHostForTesting(RenderWidgetHost* override);
 
-  // Starts the copy from the backing store.  Must be run on the UI
-  // BrowserThread.  |done_cb| is invoked with result status.  When successful
-  // (OK), the bitmap of the capture is transferred to the callback along with
-  // the timestamp at which the capture was completed.
-  void StartCopy(int frame_number, int desired_width, int desired_height,
-                 const DoneCB& done_cb);
+  // Starts the copy from the backing store. Must be run on the UI
+  // BrowserThread. Resulting frame is conveyed back to |consumer|.
+  void StartCopy(CaptureMachine* consumer,
+                 int frame_number,
+                 int desired_width,
+                 int desired_height);
 
+  // content::WebContentsObserver implementation.
   virtual void DidShowFullscreenWidget(int routing_id) OVERRIDE {
     DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
     fullscreen_widget_id_ = routing_id;
   }
 
   virtual void DidDestroyFullscreenWidget(int routing_id) OVERRIDE {
     DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
     DCHECK_EQ(fullscreen_widget_id_, routing_id);
     fullscreen_widget_id_ = MSG_ROUTING_NONE;
   }
 
  private:
   void LookUpAndObserveWebContents();
 
-  void CopyFromBackingStoreComplete(int frame_number,
-                                    const DoneCB& done_cb,
-                                    bool success,
-                                    const SkBitmap& result);
+  // Response callback for RenderWidgetHost::CopyFromBackingStore.
+  void DidCopyFromBackingStore(CaptureMachine* consumer,
+                               int frame_number,
+                               const base::Time& start_time,
+                               bool success,
+                               const SkBitmap& frame);
+
+  // Response callback for RenderWidgetHost::CopyFromBackingStoreToVideoFrame.
+  void DidCopyFromBackingStoreToVideoFrame(
+      CaptureMachine* consumer,
+      int frame_number,
+      const base::Time& start_time,
+      media::VideoFrame* frame);
 
   // The "starting point" to find the capture source.
   const int render_process_id_;
   const int render_view_id_;
 
   // Routing ID of any active fullscreen render widget or MSG_ROUTING_NONE
   // otherwise.
   int fullscreen_widget_id_;
 
   // Last known RenderView size.
@@ skipping 49 matching lines @@
 class SynchronizedConsumer {
  public:
   SynchronizedConsumer();
 
   void SetConsumer(media::VideoCaptureDevice::EventHandler* consumer);
 
   void OnFrameInfo(const media::VideoCaptureCapability& info);
   void OnError();
   void OnIncomingCapturedFrame(const uint8* pixels, int size,
                                const base::Time& timestamp);
+  void OnIncomingCapturedVideoFrame(media::VideoFrame* video_frame,
+                                    const base::Time& timestamp);
 
  private:
   base::Lock consumer_lock_;
   media::VideoCaptureDevice::EventHandler* wrapped_consumer_;
 
   DISALLOW_COPY_AND_ASSIGN(SynchronizedConsumer);
 };
 
 // Delivers rendered video frames to a consumer on a separate thread.  Also
 // responsible for logging the effective frame rate.
 class VideoFrameDeliverer {
  public:
   explicit VideoFrameDeliverer(SynchronizedConsumer* consumer);
 
+  // Deliver a fully rendered ARGB frame, using SkBitmap as a container.
+  // |done_cb| will be invoked after delivery is complete.
   void Deliver(int frame_number,
-               const SkBitmap& frame_buffer, const base::Time& frame_timestamp,
+               const SkBitmap& frame_buffer,
+               const base::Time& frame_timestamp,
                const base::Closure& done_cb);
+  // Deliver a fully rendered frame YV12 frame, using VideoFrame as a container.
+  // A refcount is taken on |frame| until delivery is complete.
+  void Deliver(int frame_number,
+               media::VideoFrame* frame,
+               const base::Time& frame_timestamp);
 
  private:
   void DeliverOnDeliverThread(int frame_number,
-                              const SkBitmap& frame_buffer,
+                              const SkBitmap& frame,
                               const base::Time& frame_timestamp,
                               const base::Closure& done_cb);
+  void DeliverVideoFrameOnDeliverThread(int frame_number,
+                                        media::VideoFrame* frame,
+                                        const base::Time& frame_timestamp);
+
+  // Treat |frame_number| as having been delivered, and update the
+  // frame rate statistics accordingly.
+  void ChronicleFrameDelivery(int frame_number);
 
   base::Thread deliver_thread_;
   SynchronizedConsumer* const consumer_;
 
   // The following keep track of and log the effective frame rate (from the
   // deliver stage) whenever verbose logging is turned on.
   base::Time last_frame_rate_log_time_;
   int count_frames_rendered_;
   int last_frame_number_;
 
@@ skipping 31 matching lines @@
     fullscreen_widget_id_ = static_cast<WebContentsImpl*>(web_contents())->
         GetFullscreenWidgetRoutingID();
   }
 }
 
 void BackingStoreCopier::SetRenderWidgetHostForTesting(
     RenderWidgetHost* override) {
   rwh_for_testing_ = override;
 }
 
-void BackingStoreCopier::StartCopy(int frame_number,
-                                   int desired_width, int desired_height,
-                                   const DoneCB& done_cb) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
-
-  TRACE_EVENT_ASYNC_BEGIN1("mirroring", "Capture", this,
-                           "frame_number", frame_number);
-
-  RenderWidgetHost* rwh;
-  if (rwh_for_testing_) {
-    rwh = rwh_for_testing_;
-  } else {
-    if (!web_contents()) {  // No source yet.
-      LookUpAndObserveWebContents();
-      if (!web_contents()) {  // No source ever.
-        done_cb.Run(NO_SOURCE, SkBitmap(), base::Time());
-        return;
-      }
-    }
-
-    if (fullscreen_widget_id_ != MSG_ROUTING_NONE) {
-      RenderProcessHost* process = web_contents()->GetRenderProcessHost();
-      rwh = process ? process->GetRenderWidgetHostByID(fullscreen_widget_id_)
-                    : NULL;
-    } else {
-      rwh = web_contents()->GetRenderViewHost();
-    }
-
-    if (!rwh) {
-      // Transient failure state (e.g., a RenderView is being replaced).
-      done_cb.Run(TRANSIENT_ERROR, SkBitmap(), base::Time());
-      return;
-    }
-  }
-
-  gfx::Size fitted_size;
-  if (RenderWidgetHostView* const view = rwh->GetView()) {
-    const gfx::Size& view_size = view->GetViewBounds().size();
-    if (!view_size.IsEmpty()) {
-      CalculateFittedSize(view_size.width(), view_size.height(),
-                          desired_width, desired_height,
-                          &fitted_size);
-    }
-    if (view_size != last_view_size_) {
-      last_view_size_ = view_size;
-
-      // Measure the number of kilopixels.
-      UMA_HISTOGRAM_COUNTS_10000(
-          "TabCapture.ViewChangeKiloPixels",
-          view_size.width() * view_size.height() / 1024);
-    }
-  }
-
-  rwh->CopyFromBackingStore(
-      gfx::Rect(),
-      fitted_size,
-      base::Bind(&BackingStoreCopier::CopyFromBackingStoreComplete,
-                 base::Unretained(this),
-                 frame_number, done_cb));
-
-  // TODO(miu): When a tab is not visible to the user, rendering stops.  For
-  // mirroring, however, it's important that rendering continues to happen.
-}
-
-void BackingStoreCopier::CopyFromBackingStoreComplete(
-    int frame_number,
-    const DoneCB& done_cb,
-    bool success,
-    const SkBitmap& frame) {
-  // Note: No restriction on which thread invokes this method but, currently,
-  // it's always the UI BrowserThread.
-  TRACE_EVENT_ASYNC_END1("mirroring", "Capture", this,
-                         "frame_number", frame_number);
-  if (success) {
-    done_cb.Run(OK, frame, base::Time::Now());
-  } else {
-    // Capture can fail due to transient issues, so just skip this frame.
-    DVLOG(1) << "CopyFromBackingStore was not successful; skipping frame.";
-    done_cb.Run(TRANSIENT_ERROR, SkBitmap(), base::Time());
-  }
-}
-
 VideoFrameRenderer::VideoFrameRenderer()
     : render_thread_("WebContentsVideo_RenderThread") {
   output_[0].in_use = false;
   output_[1].in_use = false;
   render_thread_.Start();
 }
 
 void VideoFrameRenderer::Render(int frame_number,
                                 const SkBitmap& capture,
                                 int frame_width, int frame_height,
@@ skipping 149 matching lines @@
 }
 
 void SynchronizedConsumer::OnIncomingCapturedFrame(
     const uint8* pixels, int size, const base::Time& timestamp) {
   base::AutoLock guard(consumer_lock_);
   if (wrapped_consumer_) {
     wrapped_consumer_->OnIncomingCapturedFrame(pixels, size, timestamp);
   }
 }
 
+void SynchronizedConsumer::OnIncomingCapturedVideoFrame(
+    media::VideoFrame* video_frame,
+    const base::Time& timestamp) {
+  base::AutoLock guard(consumer_lock_);
+  if (wrapped_consumer_) {
+    wrapped_consumer_->OnIncomingCapturedVideoFrame(video_frame, timestamp);
+  }
+}
+
 VideoFrameDeliverer::VideoFrameDeliverer(SynchronizedConsumer* consumer)
     : deliver_thread_("WebContentsVideo_DeliverThread"),
       consumer_(consumer),
       last_frame_number_(0) {
   DCHECK(consumer_);
   deliver_thread_.Start();
 }
 
 void VideoFrameDeliverer::Deliver(
     int frame_number,
     const SkBitmap& frame_buffer, const base::Time& frame_timestamp,
     const base::Closure& done_cb) {
   deliver_thread_.message_loop()->PostTask(
       FROM_HERE,
       base::Bind(&VideoFrameDeliverer::DeliverOnDeliverThread,
                  base::Unretained(this),
                  frame_number, base::ConstRef(frame_buffer), frame_timestamp,
                  done_cb));
 }
 
+void VideoFrameDeliverer::Deliver(
+    int frame_number,
+    media::VideoFrame* frame, const base::Time& frame_timestamp) {
+  deliver_thread_.message_loop()->PostTask(
+      FROM_HERE,
+      base::Bind(&VideoFrameDeliverer::DeliverVideoFrameOnDeliverThread,
+                 base::Unretained(this),
+                 frame_number, make_scoped_refptr(frame), frame_timestamp));
+}
+
 void VideoFrameDeliverer::DeliverOnDeliverThread(
     int frame_number,
     const SkBitmap& frame_buffer, const base::Time& frame_timestamp,
     const base::Closure& done_cb) {
   DCHECK_EQ(deliver_thread_.message_loop(), MessageLoop::current());
 
   TRACE_EVENT1("mirroring", "DeliverFrame", "frame_number", frame_number);
 
   // Send the frame to the consumer.
   // Note: The consumer will do an ARGB-->YUV conversion in this callback,
   // blocking the current thread for a bit.
   SkAutoLockPixels frame_buffer_locker(frame_buffer);
   consumer_->OnIncomingCapturedFrame(
       static_cast<const uint8*>(frame_buffer.getPixels()),
       frame_buffer.getSize(),
       frame_timestamp);
 
+  ChronicleFrameDelivery(frame_number);
+
+  // All done.
+  done_cb.Run();
+}
+
+void VideoFrameDeliverer::DeliverVideoFrameOnDeliverThread(
+    int frame_number,
+    media::VideoFrame* frame, const base::Time& frame_timestamp) {
+  DCHECK_EQ(deliver_thread_.message_loop(), MessageLoop::current());
+
+  TRACE_EVENT1("mirroring", "DeliverFrame", "frame_number", frame_number);
+
+  // Send the frame to the consumer.
+  consumer_->OnIncomingCapturedVideoFrame(frame, frame_timestamp);
+
+  ChronicleFrameDelivery(frame_number);
+}
+
+void VideoFrameDeliverer::ChronicleFrameDelivery(int frame_number) {
   // Log frame rate, if verbose logging is turned on.
   static const base::TimeDelta kFrameRateLogInterval =
       base::TimeDelta::FromSeconds(10);
   const base::Time& now = base::Time::Now();
   if (last_frame_rate_log_time_.is_null()) {
     last_frame_rate_log_time_ = now;
     count_frames_rendered_ = 0;
     last_frame_number_ = frame_number;
   } else {
     ++count_frames_rendered_;
@@ skipping 10 matching lines @@
       UMA_HISTOGRAM_COUNTS(
           "TabCapture.FrameRate",
           static_cast<int>(measured_fps));
       VLOG(1) << "Current measured frame rate for CaptureMachine@" << this
               << " is " << measured_fps << " FPS.";
       last_frame_rate_log_time_ = now;
       count_frames_rendered_ = 0;
       last_frame_number_ = frame_number;
     }
   }
-
-  // All done.
-  done_cb.Run();
 }
 
 }  // namespace
 
 // The "meat" of the video capture implementation, which is a ref-counted class.
 // Separating this from the "shell class" WebContentsVideoCaptureDevice allows
 // safe destruction without needing to block any threads (e.g., the IO
 // BrowserThread).
 //
 // CaptureMachine manages a simple state machine and the pipeline (see notes at
 // top of this file).  It times the start of successive captures and
 // facilitates the processing of each through the stages of the pipeline.
 class CaptureMachine
     : public base::RefCountedThreadSafe<CaptureMachine, CaptureMachine> {
  public:
+  enum SnapshotError {
+    NO_SOURCE,
+    TRANSIENT_ERROR
+  };
+
   CaptureMachine(int render_process_id, int render_view_id);
 
   // Sets the capture source to the given |override| for unit testing.
   // Also, |destroy_cb| will be invoked after CaptureMachine is fully destroyed
   // (to synchronize tear-down).
   void InitializeForTesting(RenderWidgetHost* override,
                             const base::Closure& destroy_cb);
 
   // Synchronously sets/unsets the consumer.  Pass |consumer| as NULL to remove
   // the reference to the consumer; then, once this method returns,
   // CaptureMachine will no longer invoke callbacks on the old consumer from any
   // thread.
   void SetConsumer(media::VideoCaptureDevice::EventHandler* consumer);
 
   // Asynchronous requests to change CaptureMachine state.
   void Allocate(int width, int height, int frame_rate);
   void Start();
   void Stop();
   void DeAllocate();
 
+  // Snapshot result events.
+  void OnSnapshotComplete(int frame_number,
+                          const base::Time& start_time,
+                          const base::TimeDelta& duration,
+                          const SkBitmap& frame);
+  void OnSnapshotComplete(int frame_number,
+                          const base::Time& start_time,
+                          const base::TimeDelta& duration,
+                          media::VideoFrame* frame);
+  void OnSnapshotFailed(SnapshotError error,
+                        int frame_number);
+
  private:
   friend class base::RefCountedThreadSafe<CaptureMachine, CaptureMachine>;
 
   // Flag indicating current state.
   enum State {
     kIdle,
     kAllocated,
     kCapturing,
     kError,
     kDestroyed
   };
 
   virtual ~CaptureMachine();
 
   void TransitionStateTo(State next_state);
 
   // Stops capturing and notifies consumer_ of an error state.
   void Error();
 
   // Schedules the next frame capture off of the system clock, skipping frames
   // to catch-up if necessary.
   void ScheduleNextFrameCapture();
 
   // The glue between the pipeline stages.
   void StartSnapshot();
-  void SnapshotComplete(int frame_number,
-                        const base::Time& start_time,
-                        BackingStoreCopier::Result result,
-                        const SkBitmap& capture,
-                        const base::Time& capture_time);
+  bool FinishSnapshot();
+  void SnapshotCompleteBitmap(int frame_number,
+                              const base::Time& start_time,
+                              const base::TimeDelta& duration,
+                              const SkBitmap& frame);
+  void SnapshotCompleteVideoFrame(int frame_number,
+                                  const base::Time& start_time,
+                                  const base::TimeDelta& duration,
+                                  media::VideoFrame* frame);
+  void SnapshotFailed(SnapshotError error, int frame_number);
+
   void RenderComplete(int frame_number,
                       const base::Time& capture_time,
                       const SkBitmap* frame_buffer);
   void DeliverComplete(const SkBitmap* frame_buffer);
 
   // Specialized RefCounted traits for CaptureMachine, so that operator delete
   // is called from an "outside" thread.  See comments for "traits" in
   // base/memory/ref_counted.h.
   static void Destruct(const CaptureMachine* x);
   static void DeleteFromOutsideThread(const CaptureMachine* x);
@@ skipping 67 matching lines @@
   if (width < kMinFrameWidth || height < kMinFrameHeight) {
     DVLOG(1) << "invalid width (" << width << ") and/or height ("
              << height << ")";
     Error();
     return;
   }
 
   settings_.width = width;
   settings_.height = height;
   settings_.frame_rate = frame_rate;
+  // Sets the color format used by OnIncomingCapturedFrame.
+  // Does not apply to OnIncomingCapturedVideoFrame.
   settings_.color = media::VideoCaptureCapability::kARGB;
   settings_.expected_capture_delay = 0;
   settings_.interlaced = false;
 
   capture_period_ = base::TimeDelta::FromMicroseconds(
       1000000.0 / settings_.frame_rate + 0.5);
 
   consumer_.OnFrameInfo(settings_);
 
   TransitionStateTo(kAllocated);
@@ skipping 124 matching lines @@
 void CaptureMachine::StartSnapshot() {
   DCHECK_EQ(manager_thread_.message_loop(), MessageLoop::current());
 
   if (state_ != kCapturing) {
     return;
   }
 
   if (!is_snapshotting_) {
     is_snapshotting_ = true;
 
-    const BackingStoreCopier::DoneCB& done_cb =
-        media::BindToLoop(manager_thread_.message_loop_proxy(),
-                          base::Bind(&CaptureMachine::SnapshotComplete, this,
-                                     frame_number_, base::Time::Now()));
-    const base::Closure& start_cb =
+    BrowserThread::PostTask(BrowserThread::UI, FROM_HERE,
         base::Bind(&BackingStoreCopier::StartCopy,
-                   base::Unretained(&copier_),
-                   frame_number_, settings_.width, settings_.height, done_cb);
-    BrowserThread::PostTask(BrowserThread::UI, FROM_HERE, start_cb);
+                   base::Unretained(&copier_), make_scoped_refptr(this),
+                   frame_number_, settings_.width, settings_.height)
+      );
   }
 
   ScheduleNextFrameCapture();
 }
 
-void CaptureMachine::SnapshotComplete(int frame_number,
-                                      const base::Time& start_time,
-                                      BackingStoreCopier::Result result,
-                                      const SkBitmap& capture,
-                                      const base::Time& capture_time) {
+bool CaptureMachine::FinishSnapshot() {
+  DCHECK_EQ(manager_thread_.message_loop(), MessageLoop::current());
+
+  DCHECK(is_snapshotting_);
+  is_snapshotting_ = false;
+
+  return state_ == kCapturing;
+}
+
+void CaptureMachine::OnSnapshotComplete(int frame_number,
+                                        const base::Time& start_time,
+                                        const base::TimeDelta& duration,
+                                        const SkBitmap& frame) {
+  manager_thread_.message_loop()->PostTask(FROM_HERE,
+      base::Bind(&CaptureMachine::SnapshotCompleteBitmap, this,
+                 frame_number, start_time, duration, frame));
+}
+
+void CaptureMachine::SnapshotCompleteBitmap(int frame_number,
+                                            const base::Time& start_time,
+                                            const base::TimeDelta& duration,
+                                            const SkBitmap& capture) {
+  if (!FinishSnapshot())
+    return;
+
+  UMA_HISTOGRAM_TIMES("TabCapture.SnapshotTime", duration);
+  if (num_renders_pending_ <= 1) {
+    ++num_renders_pending_;
+    renderer_.Render(
+        frame_number,
+        capture,
+        settings_.width, settings_.height,
+        media::BindToLoop(manager_thread_.message_loop_proxy(),
+                          base::Bind(&CaptureMachine::RenderComplete, this,
+                                     frame_number, start_time + duration)));
+  }
+}
+
+void CaptureMachine::OnSnapshotComplete(int frame_number,
+                                        const base::Time& start_time,
+                                        const base::TimeDelta& duration,
+                                        media::VideoFrame* frame) {
+  manager_thread_.message_loop()->PostTask(FROM_HERE,
+      base::Bind(&CaptureMachine::SnapshotCompleteVideoFrame, this,
+                 frame_number, start_time, duration,
+                 make_scoped_refptr(frame)));
+}
+
+void CaptureMachine::SnapshotCompleteVideoFrame(
+    int frame_number,
+    const base::Time& start_time,
+    const base::TimeDelta& duration,
+    media::VideoFrame* frame) {
+  if (!FinishSnapshot())
+    return;
+
+  UMA_HISTOGRAM_TIMES("TabCapture.SnapshotTime", duration);
+
+  deliverer_.Deliver(frame_number, frame, start_time + duration);
+}
+
+void CaptureMachine::OnSnapshotFailed(CaptureMachine::SnapshotError error,
+                                      int frame_number) {
+  manager_thread_.message_loop()->PostTask(FROM_HERE,
+      base::Bind(&CaptureMachine::SnapshotFailed, this, error, frame_number));
+}
+
+void CaptureMachine::SnapshotFailed(CaptureMachine::SnapshotError error,
+                                    int frame_number) {
   DCHECK_EQ(manager_thread_.message_loop(), MessageLoop::current());
 
   DCHECK(is_snapshotting_);
   is_snapshotting_ = false;
 
   if (state_ != kCapturing) {
     return;
   }
 
-  switch (result) {
-    case BackingStoreCopier::OK:
-      UMA_HISTOGRAM_TIMES("TabCapture.SnapshotTime",
-                          base::Time::Now() - start_time);
-      if (num_renders_pending_ <= 1) {
-        ++num_renders_pending_;
-        DCHECK(!capture_time.is_null());
-        renderer_.Render(
-            frame_number,
-            capture,
-            settings_.width, settings_.height,
-            media::BindToLoop(manager_thread_.message_loop_proxy(),
-                              base::Bind(&CaptureMachine::RenderComplete, this,
-                                         frame_number, capture_time)));
-      }
-      break;
-
-    case BackingStoreCopier::TRANSIENT_ERROR:
-      // Skip this frame.
-      break;
-
-    case BackingStoreCopier::NO_SOURCE:
-      DVLOG(1) << "no capture source";
-      Error();
-      break;
-  }
+  if (error == NO_SOURCE)
+    Error();
 }
 
 void CaptureMachine::RenderComplete(int frame_number,
                                     const base::Time& capture_time,
                                     const SkBitmap* frame_buffer) {
   DCHECK_EQ(manager_thread_.message_loop(), MessageLoop::current());
 
   --num_renders_pending_;
   DCHECK_LE(0, num_renders_pending_);
 
   if (state_ != kCapturing || !frame_buffer) {
     return;
   }
 
   DCHECK(!capture_time.is_null());
   DCHECK(frame_buffer);
   deliverer_.Deliver(
       frame_number, *frame_buffer, capture_time,
       base::Bind(&CaptureMachine::DeliverComplete, this, frame_buffer));
 }
 
 void CaptureMachine::DeliverComplete(const SkBitmap* frame_buffer) {
   renderer_.Release(frame_buffer);
 }
 
+void BackingStoreCopier::StartCopy(CaptureMachine* consumer,
+                                   int frame_number,
+                                   int desired_width,
+                                   int desired_height) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+
+  RenderWidgetHost* rwh;
+  if (rwh_for_testing_) {
+    rwh = rwh_for_testing_;
+  } else {
+    if (!web_contents()) {  // No source yet.
+      LookUpAndObserveWebContents();
+      if (!web_contents()) {  // No source ever.
+        consumer->OnSnapshotFailed(CaptureMachine::NO_SOURCE, frame_number);
+        return;
+      }
+    }
+
+    if (fullscreen_widget_id_ != MSG_ROUTING_NONE) {
+      RenderProcessHost* process = web_contents()->GetRenderProcessHost();
+      rwh = process ? process->GetRenderWidgetHostByID(fullscreen_widget_id_)
+                    : NULL;
+    } else {
+      rwh = web_contents()->GetRenderViewHost();
+    }
+
+    if (!rwh) {
+      // Transient failure state (e.g., a RenderView is being replaced).
+      consumer->OnSnapshotFailed(CaptureMachine::TRANSIENT_ERROR, frame_number);
+      return;
+    }
+  }
+
+  gfx::Size fitted_size;
+  if (RenderWidgetHostView* const view = rwh->GetView()) {
+    const gfx::Size& view_size = view->GetViewBounds().size();
+    if (!view_size.IsEmpty()) {
+      CalculateFittedSize(view_size.width(), view_size.height(),
+                          desired_width, desired_height,
+                          &fitted_size);
+    }
+    if (view_size != last_view_size_) {
+      last_view_size_ = view_size;
+
+      // Measure the number of kilopixels.
+      UMA_HISTOGRAM_COUNTS_10000(
+          "TabCapture.ViewChangeKiloPixels",
+          view_size.width() * view_size.height() / 1024);
+    }
+  }
+
+  TRACE_EVENT_ASYNC_BEGIN1("mirroring", "Capture", this,
+                           "frame_number", frame_number);
+  if (rwh->CanCopyToVideoFrame()) {
+    rwh->CopyFromBackingStoreToVideoFrame(
+        gfx::Rect(),
+        gfx::Size(desired_width, desired_height),
+        base::Bind(&BackingStoreCopier::DidCopyFromBackingStoreToVideoFrame,
+                   base::Unretained(this), make_scoped_refptr(consumer),
+                   frame_number, base::Time::Now()));
+  } else {
+    rwh->CopyFromBackingStore(
+        gfx::Rect(),
+        fitted_size,
+        base::Bind(&BackingStoreCopier::DidCopyFromBackingStore,
+                   base::Unretained(this), make_scoped_refptr(consumer),
+                   frame_number, base::Time::Now()));
+  }
+  // TODO(miu): When a tab is not visible to the user, rendering stops.  For
+  // mirroring, however, it's important that rendering continues to happen.
+}
+
+void BackingStoreCopier::DidCopyFromBackingStore(
+    CaptureMachine* consumer,
+    int frame_number,
+    const base::Time& start_time,
+    bool success,
+    const SkBitmap& frame) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+  // Note: No restriction on which thread invokes this method but, currently,
+  // it's always the UI BrowserThread.
+  TRACE_EVENT_ASYNC_END1("mirroring", "Capture", this,
+                         "frame_number", frame_number);
+
+  if (success) {
+    consumer->OnSnapshotComplete(
+        frame_number, start_time, base::Time::Now() - start_time, frame);
+  } else {
+    // Capture can fail due to transient issues, so just skip this frame.
+    DVLOG(1) << "CopyFromBackingStore was not successful; skipping frame.";
+    consumer->OnSnapshotFailed(CaptureMachine::TRANSIENT_ERROR, frame_number);
+  }
+}
+
+void BackingStoreCopier::DidCopyFromBackingStoreToVideoFrame(
+    CaptureMachine* consumer,
+    int frame_number,
+    const base::Time& start_time,
+    media::VideoFrame* frame) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+  // Note: No restriction on which thread invokes this method but, currently,
+  // it's always the UI BrowserThread.
+  TRACE_EVENT_ASYNC_END1("mirroring", "Capture", this,
+                         "frame_number", frame_number);
+
+  if (frame && frame->format() != media::VideoFrame::INVALID &&
+      frame->format() != media::VideoFrame::EMPTY) {
+    consumer->OnSnapshotComplete(
+        frame_number, start_time, base::Time::Now() - start_time, frame);
+  } else {
+    // Capture can fail due to transient issues, so just skip this frame.
+    DVLOG(1) << "CopyFromBackingStoreToVideoFrame failure; skipping frame.";
+    consumer->OnSnapshotFailed(
+        CaptureMachine::TRANSIENT_ERROR, frame_number);
+  }
+}
+
 WebContentsVideoCaptureDevice::WebContentsVideoCaptureDevice(
     const media::VideoCaptureDevice::Name& name,
     int render_process_id, int render_view_id)
     : device_name_(name),
       capturer_(new CaptureMachine(render_process_id, render_view_id)) {}
 
 WebContentsVideoCaptureDevice::WebContentsVideoCaptureDevice(
     RenderWidgetHost* test_source, const base::Closure& destroy_cb)
     : capturer_(new CaptureMachine(-1, -1)) {
   device_name_.device_name = "WebContentsForTesting";
@@ skipping 55 matching lines @@
   capturer_->SetConsumer(NULL);
   capturer_->DeAllocate();
 }
 
 const media::VideoCaptureDevice::Name&
 WebContentsVideoCaptureDevice::device_name() {
   return device_name_;
 }
 
 }  // namespace content