Use webrtc::DesktopCapturer for screen capturer implementation.

media/video/capture/screen/screen_capturer_x11.cc

Index: media/video/capture/screen/screen_capturer_x11.cc
diff --git a/media/video/capture/screen/screen_capturer_x11.cc b/media/video/capture/screen/screen_capturer_x11.cc
index f9da3b3533e4e1ede7054ba59da750c3187e43ab..826b59347a7b5db9e58cd6860e4da4499db2a577 100644
--- a/media/video/capture/screen/screen_capturer_x11.cc
+++ b/media/video/capture/screen/screen_capturer_x11.cc
@@ -15,32 +15,17 @@
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/stl_util.h"
-#include "base/time.h"
 #include "media/video/capture/screen/differ.h"
 #include "media/video/capture/screen/mouse_cursor_shape.h"
-#include "media/video/capture/screen/screen_capture_data.h"
-#include "media/video/capture/screen/screen_capture_frame.h"
 #include "media/video/capture/screen/screen_capture_frame_queue.h"
 #include "media/video/capture/screen/screen_capturer_helper.h"
 #include "media/video/capture/screen/x11/x_server_pixel_buffer.h"
+#include "third_party/webrtc/modules/desktop_capture/desktop_frame.h"
 
 namespace media {
 
 namespace {
 
-// A class representing a full-frame pixel buffer.
-class ScreenCaptureFrameLinux : public ScreenCaptureFrame {
- public:
-  explicit ScreenCaptureFrameLinux(const SkISize& window_size);
-  virtual ~ScreenCaptureFrameLinux();
-
- private:
-  // Allocated pixel buffer.
-  scoped_ptr<uint8[]> data_;
-
-  DISALLOW_COPY_AND_ASSIGN(ScreenCaptureFrameLinux);
-};
-
 // A class to perform video frame capturing for Linux.
 class ScreenCapturerLinux : public ScreenCapturer {
  public:
@@ -50,9 +35,13 @@ class ScreenCapturerLinux : public ScreenCapturer {
   // TODO(ajwong): Do we really want this to be synchronous?
   bool Init(bool use_x_damage);
 
-  // Capturer interface.
-  virtual void Start(Delegate* delegate) OVERRIDE;
-  virtual void CaptureFrame() OVERRIDE;
+  // DesktopCapturer interface.
+  virtual void Start(Callback* delegate) OVERRIDE;
+  virtual void Capture(const webrtc::DesktopRegion& region) OVERRIDE;
+
+  // ScreenCapturer interface.
+  virtual void SetMouseShapeObserver(
+      MouseShapeObserver* mouse_shape_observer) OVERRIDE;
 
  private:
   void InitXDamage();
@@ -67,17 +56,16 @@ class ScreenCapturerLinux : public ScreenCapturer {
   // Capture the cursor image and notify the delegate if it was captured.
   void CaptureCursor();
 
-  // Capture screen pixels, and return the data in a new ScreenCaptureData
-  // object, to be freed by the caller. In the DAMAGE case, the
-  // ScreenCapturerHelper already holds the list of invalid rectangles from
-  // ProcessPendingXEvents(). In the non-DAMAGE case, this captures the whole
-  // screen, then calculates some invalid rectangles that include any
+  // Capture screen pixels in the current buffer in the queue. In the DAMAGE

[alexeypa (please no reviews), 2013/04/26 21:33:58]

nit: "to the current buffer". 

[Sergey Ulanov, 2013/05/07 22:25:50]

Done.

+  // case, the ScreenCapturerHelper already holds the list of invalid rectangles
+  // from ProcessPendingXEvents(). In the non-DAMAGE case, this captures the
+  // whole screen, then calculates some invalid rectangles that include any
   // differences between this and the previous capture.
-  scoped_refptr<ScreenCaptureData> CaptureScreen();
+  void CaptureScreen();
 
   // Called when the screen configuration is changed. |root_window_size|
   // specifies the most recent size of the root window.
-  void ScreenConfigurationChanged(const SkISize& root_window_size);
+  void ScreenConfigurationChanged(const webrtc::DesktopSize& root_window_size);
 
   // Synchronize the current buffer with |last_buffer_|, by copying pixels from
   // the area of |last_invalid_rects|.
@@ -89,24 +77,27 @@ class ScreenCapturerLinux : public ScreenCapturer {
   void DeinitXlib();
 
   // Capture a rectangle from |x_server_pixel_buffer_|, and copy the data into
-  // |capture_data|.
-  void CaptureRect(const SkIRect& rect, ScreenCaptureData* capture_data);
+  // |frame|.
+  void CaptureRect(const webrtc::DesktopRect& rect,
+                   webrtc::DesktopFrame* frame);
 
   // We expose two forms of blitting to handle variations in the pixel format.
   // In FastBlit, the operation is effectively a memcpy.
   void FastBlit(uint8* image,
-                const SkIRect& rect,
-                ScreenCaptureData* capture_data);
+                const webrtc::DesktopRect& rect,
+                webrtc::DesktopFrame* frame);
   void SlowBlit(uint8* image,
-                const SkIRect& rect,
-                ScreenCaptureData* capture_data);
+                const webrtc::DesktopRect& rect,
+                webrtc::DesktopFrame* frame);
 
   // Returns the number of bits |mask| has to be shifted left so its last
   // (most-significant) bit set becomes the most-significant bit of the word.
   // When |mask| is 0 the function returns 31.
   static uint32 GetRgbShift(uint32 mask);
 
-  Delegate* delegate_;
+  Callback* callback_;
+

[alexeypa (please no reviews), 2013/04/26 21:33:58]

nit: no need for this empty line.

[Sergey Ulanov, 2013/05/07 22:25:50]

Done.

+  MouseShapeObserver* mouse_shape_observer_;
 
   // X11 graphics context.
   Display* display_;
@@ -114,7 +105,7 @@ class ScreenCapturerLinux : public ScreenCapturer {
   Window root_window_;
 
   // Last known dimensions of the root window.
-  SkISize root_window_size_;
+  webrtc::DesktopSize root_window_size_;
 
   // XFixes.
   bool has_xfixes_;
@@ -140,7 +131,7 @@ class ScreenCapturerLinux : public ScreenCapturer {
 
   // Invalid region from the previous capture. This is used to synchronize the
   // current with the last buffer used.
-  SkRegion last_invalid_region_;
+  webrtc::DesktopRegion last_invalid_region_;
 
   // |Differ| for use when polling for changes.
   scoped_ptr<Differ> differ_;
@@ -148,24 +139,12 @@ class ScreenCapturerLinux : public ScreenCapturer {
   DISALLOW_COPY_AND_ASSIGN(ScreenCapturerLinux);
 };
 
-ScreenCaptureFrameLinux::ScreenCaptureFrameLinux(const SkISize& window_size) {
-  set_bytes_per_row(window_size.width() * ScreenCaptureData::kBytesPerPixel);
-  set_dimensions(window_size);
-
-  size_t buffer_size = bytes_per_row() * window_size.height();
-  data_.reset(new uint8[buffer_size]);
-  set_pixels(data_.get());
-}
-
-ScreenCaptureFrameLinux::~ScreenCaptureFrameLinux() {
-}
-
 ScreenCapturerLinux::ScreenCapturerLinux()
-    : delegate_(NULL),
+    : callback_(NULL),
+      mouse_shape_observer_(NULL),
       display_(NULL),
       gc_(NULL),
       root_window_(BadValue),
-      root_window_size_(SkISize::Make(0, 0)),
       has_xfixes_(false),
       xfixes_event_base_(-1),
       xfixes_error_base_(-1),
@@ -270,50 +249,49 @@ void ScreenCapturerLinux::InitXDamage() {
   LOG(INFO) << "Using XDamage extension.";
 }
 
-void ScreenCapturerLinux::Start(Delegate* delegate) {
-  DCHECK(delegate_ == NULL);
+void ScreenCapturerLinux::Start(Callback* callback) {
+  DCHECK(callback_ == NULL);

[alexeypa (please no reviews), 2013/04/26 21:33:58]

DCHECK(!callback_);
DCHECK(callback);

[Sergey Ulanov, 2013/05/07 22:25:50]

Done.

 
-  delegate_ = delegate;
+  callback_ = callback;
 }
 
-void ScreenCapturerLinux::CaptureFrame() {
+void ScreenCapturerLinux::Capture(const webrtc::DesktopRegion& region) {
   base::Time capture_start_time = base::Time::Now();
 
   // Process XEvents for XDamage and cursor shape tracking.
   ProcessPendingXEvents();
 
-  // If the current buffer is from an older generation then allocate a new one.
+  // If the current frame is from an older generation then allocate a new one.
   // Note that we can't reallocate other buffers at this point, since the caller
   // may still be reading from them.
   if (queue_.current_frame_needs_update()) {
-    scoped_ptr<ScreenCaptureFrameLinux> buffer(new ScreenCaptureFrameLinux(
-        root_window_size_));
-    queue_.ReplaceCurrentFrame(buffer.PassAs<ScreenCaptureFrame>());
+    scoped_ptr<webrtc::DesktopFrame> frame(
+        new webrtc::BasicDesktopFrame(root_window_size_));
+    queue_.ReplaceCurrentFrame(frame.Pass());
   }
 
   // Refresh the Differ helper used by CaptureFrame(), if needed.
-  const ScreenCaptureFrame* current_buffer = queue_.current_frame();
+  webrtc::DesktopFrame* frame = queue_.current_frame();
   if (!use_damage_ && (
       !differ_.get() ||
-      (differ_->width() != current_buffer->dimensions().width()) ||
-      (differ_->height() != current_buffer->dimensions().height()) ||
-      (differ_->bytes_per_row() != current_buffer->bytes_per_row()))) {
-    differ_.reset(new Differ(current_buffer->dimensions().width(),
-                             current_buffer->dimensions().height(),
-                             ScreenCaptureData::kBytesPerPixel,
-                             current_buffer->bytes_per_row()));
+      (differ_->width() != frame->size().width()) ||
+      (differ_->height() != frame->size().height()) ||
+      (differ_->bytes_per_row() != frame->stride()))) {
+    differ_.reset(new Differ(frame->size().width(), frame->size().height(),
+                             webrtc::DesktopFrame::kBytesPerPixel,
+                             frame->stride()));
   }
 
-  scoped_refptr<ScreenCaptureData> capture_data(CaptureScreen());
-
-  // Swap the current & previous buffers ready for the next capture.
-  last_invalid_region_ = capture_data->dirty_region();
+  CaptureScreen();
 
-  queue_.DoneWithCurrentFrame();
-
-  capture_data->set_capture_time_ms(
+  queue_.current_frame()->set_capture_time_ms(

[alexeypa (please no reviews), 2013/04/26 21:33:58]

nit: queue_.current_frame() -> frame.

[Sergey Ulanov, 2013/05/07 22:25:50]

Done.

       (base::Time::Now() - capture_start_time).InMillisecondsRoundedUp());
-  delegate_->OnCaptureCompleted(capture_data);
+  callback_->OnCaptureCompleted(queue_.EmitCurrentFrameAndMoveToNext());
+}
+
+void ScreenCapturerLinux::SetMouseShapeObserver(
+      MouseShapeObserver* mouse_shape_observer) {
+  mouse_shape_observer_ = mouse_shape_observer;

[alexeypa (please no reviews), 2013/04/26 21:33:58]

DCHECK(!mouse_shape_observer_);
DCHECK(mouse_shape_observer);

[Sergey Ulanov, 2013/05/07 22:25:50]

Done.

 }
 
 void ScreenCapturerLinux::ProcessPendingXEvents() {
@@ -329,7 +307,8 @@ void ScreenCapturerLinux::ProcessPendingXEvents() {
       DCHECK(event->level == XDamageReportNonEmpty);
     } else if (e.type == ConfigureNotify) {
       const XConfigureEvent& event = e.xconfigure;
-      ScreenConfigurationChanged(SkISize::Make(event.width, event.height));
+      ScreenConfigurationChanged(
+          webrtc::DesktopSize(event.width, event.height));
     } else if (has_xfixes_ &&
                e.type == xfixes_event_base_ + XFixesCursorNotify) {
       XFixesCursorNotifyEvent* cne;
@@ -352,11 +331,11 @@ void ScreenCapturerLinux::CaptureCursor() {
   }
 
   scoped_ptr<MouseCursorShape> cursor(new MouseCursorShape());
-  cursor->size.set(img->width, img->height);
-  cursor->hotspot.set(img->xhot, img->yhot);
+  cursor->size = webrtc::DesktopSize(img->width, img->height);
+  cursor->hotspot = webrtc::DesktopVector(img->xhot, img->yhot);
 
-  int total_bytes = cursor->size.width() * cursor->size.height() *
-      ScreenCaptureData::kBytesPerPixel;
+  int total_bytes = cursor->size.width ()* cursor->size.height() *
+      webrtc::DesktopFrame::kBytesPerPixel;
   cursor->data.resize(total_bytes);
 
   // Xlib stores 32-bit data in longs, even if longs are 64-bits long.
@@ -368,17 +347,16 @@ void ScreenCapturerLinux::CaptureCursor() {
   }
   XFree(img);
 
-  delegate_->OnCursorShapeChanged(cursor.Pass());
+  if (mouse_shape_observer_)

[alexeypa (please no reviews), 2013/04/26 21:33:58]

Can it be NULL?

[Sergey Ulanov, 2013/05/07 22:25:50]

yes

+    mouse_shape_observer_->OnCursorShapeChanged(cursor.Pass());
 }
 
-scoped_refptr<ScreenCaptureData> ScreenCapturerLinux::CaptureScreen() {
-  ScreenCaptureFrame* frame = queue_.current_frame();
-  scoped_refptr<ScreenCaptureData> capture_data(new ScreenCaptureData(
-      frame->pixels(), frame->bytes_per_row(), frame->dimensions()));
+void ScreenCapturerLinux::CaptureScreen() {
+  webrtc::DesktopFrame* frame = queue_.current_frame();
 
   // Pass the screen size to the helper, so it can clip the invalid region if it
   // expands that region to a grid.
-  helper_.set_size_most_recent(capture_data->size());
+  helper_.set_size_most_recent(frame->size());
 
   // In the DAMAGE case, ensure the frame is up-to-date with the previous frame
   // if any.  If there isn't a previous frame, that means a screen-resolution
@@ -387,7 +365,7 @@ scoped_refptr<ScreenCaptureData> ScreenCapturerLinux::CaptureScreen() {
   if (use_damage_ && queue_.previous_frame())
     SynchronizeFrame();
 
-  SkRegion invalid_region;
+  webrtc::DesktopRegion invalid_region;
 
   x_server_pixel_buffer_.Synchronize();
   if (use_damage_ && queue_.previous_frame()) {
@@ -398,9 +376,8 @@ scoped_refptr<ScreenCaptureData> ScreenCapturerLinux::CaptureScreen() {
     XRectangle* rects = XFixesFetchRegionAndBounds(display_, damage_region_,
                                                    &nRects, &bounds);
     for (int i=0; i<nRects; ++i) {

[alexeypa (please no reviews), 2013/04/26 21:33:58]

nit: for (int i = 0; i < nRects; ++i) {

[Sergey Ulanov, 2013/05/07 22:25:50]

Done.

-      invalid_region.op(SkIRect::MakeXYWH(rects[i].x, rects[i].y,
-                                          rects[i].width, rects[i].height),
-                        SkRegion::kUnion_Op);
+      invalid_region.AddRect(webrtc::DesktopRect::MakeXYWH(
+          rects[i].x, rects[i].y, rects[i].width, rects[i].height));
     }
     XFree(rects);
     helper_.InvalidateRegion(invalid_region);
@@ -411,39 +388,41 @@ scoped_refptr<ScreenCaptureData> ScreenCapturerLinux::CaptureScreen() {
     // Clip the damaged portions to the current screen size, just in case some
     // spurious XDamage notifications were received for a previous (larger)
     // screen size.
-    invalid_region.op(SkIRect::MakeSize(root_window_size_),
-                      SkRegion::kIntersect_Op);
-    for (SkRegion::Iterator it(invalid_region); !it.done(); it.next()) {
-      CaptureRect(it.rect(), capture_data);
+    invalid_region.IntersectWith(
+        webrtc::DesktopRect::MakeSize(root_window_size_));
+    for (webrtc::DesktopRegion::Iterator it(invalid_region);
+         !it.IsAtEnd(); it.Advance()) {
+      CaptureRect(it.rect(), frame);
     }
   } else {
     // Doing full-screen polling, or this is the first capture after a
     // screen-resolution change.  In either case, need a full-screen capture.
-    SkIRect screen_rect = SkIRect::MakeWH(frame->dimensions().width(),
-                                          frame->dimensions().height());
-    CaptureRect(screen_rect, capture_data);
+    webrtc::DesktopRect screen_rect =
+        webrtc::DesktopRect::MakeSize(frame->size());
+    CaptureRect(screen_rect, frame);
 
     if (queue_.previous_frame()) {
       // Full-screen polling, so calculate the invalid rects here, based on the
       // changed pixels between current and previous buffers.
       DCHECK(differ_ != NULL);
-      differ_->CalcDirtyRegion(queue_.previous_frame()->pixels(),
-                               frame->pixels(), &invalid_region);
+      DCHECK(queue_.previous_frame()->data());
+      differ_->CalcDirtyRegion(queue_.previous_frame()->data(),
+                               frame->data(), &invalid_region);
     } else {
       // No previous buffer, so always invalidate the whole screen, whether
       // or not DAMAGE is being used.  DAMAGE doesn't necessarily send a
       // full-screen notification after a screen-resolution change, so
       // this is done here.
-      invalid_region.op(screen_rect, SkRegion::kUnion_Op);
+      invalid_region.SetRect(screen_rect);
     }
   }
 
-  capture_data->mutable_dirty_region() = invalid_region;
-  return capture_data;
+  last_invalid_region_ = invalid_region;
+  *frame->mutable_updated_region() = invalid_region;
 }
 
 void ScreenCapturerLinux::ScreenConfigurationChanged(
-    const SkISize& root_window_size) {
+    const webrtc::DesktopSize& root_window_size) {
   root_window_size_ = root_window_size;
 
   // Make sure the frame buffers will be reallocated.
@@ -464,18 +443,18 @@ void ScreenCapturerLinux::SynchronizeFrame() {
   // http://crbug.com/92354
   DCHECK(queue_.previous_frame());
 
-  ScreenCaptureFrame* current = queue_.current_frame();
-  ScreenCaptureFrame* last = queue_.previous_frame();
+  webrtc::DesktopFrame* current = queue_.current_frame();
+  webrtc::DesktopFrame* last = queue_.previous_frame();
   DCHECK_NE(current, last);
-  for (SkRegion::Iterator it(last_invalid_region_); !it.done(); it.next()) {
-    const SkIRect& r = it.rect();
-    int offset = r.fTop * current->bytes_per_row() +
-        r.fLeft * ScreenCaptureData::kBytesPerPixel;
+  for (webrtc::DesktopRegion::Iterator it(last_invalid_region_);
+       !it.IsAtEnd(); it.Advance()) {
+    const webrtc::DesktopRect& r = it.rect();
+    int offset = r.top() * current->stride() +

[alexeypa (please no reviews), 2013/04/26 21:33:58]

nit: move getting pointer to the pixel at given coordinates to DesktopFrame and
reuse it in the loop below.

[Sergey Ulanov, 2013/05/07 22:25:50]

That would require changes in DesktopFrame. I don't think it's really needed,
but we can do it later when this code is moved to webrtc.

+        r.left() * webrtc::DesktopFrame::kBytesPerPixel;
     for (int i = 0; i < r.height(); ++i) {
-      memcpy(current->pixels() + offset, last->pixels() + offset,
-             r.width() * ScreenCaptureData::kBytesPerPixel);
-      offset += current->dimensions().width() *
-          ScreenCaptureData::kBytesPerPixel;
+      memcpy(current->data() + offset, last->data() + offset,
+             r.width() * webrtc::DesktopFrame::kBytesPerPixel);
+      offset += current->size().width() * webrtc::DesktopFrame::kBytesPerPixel;
     }
   }
 }
@@ -500,8 +479,8 @@ void ScreenCapturerLinux::DeinitXlib() {
   }
 }
 
-void ScreenCapturerLinux::CaptureRect(const SkIRect& rect,
-                                      ScreenCaptureData* capture_data) {
+void ScreenCapturerLinux::CaptureRect(const webrtc::DesktopRect& rect,
+                                      webrtc::DesktopFrame* frame) {
   uint8* image = x_server_pixel_buffer_.CaptureRect(rect);
   int depth = x_server_pixel_buffer_.GetDepth();
   if ((depth == 24 || depth == 32) &&
@@ -510,35 +489,37 @@ void ScreenCapturerLinux::CaptureRect(const SkIRect& rect,
       x_server_pixel_buffer_.GetGreenMask() == 0xff00 &&
       x_server_pixel_buffer_.GetBlueMask() == 0xff) {
     DVLOG(3) << "Fast blitting";
-    FastBlit(image, rect, capture_data);
+    FastBlit(image, rect, frame);
   } else {
     DVLOG(3) << "Slow blitting";
-    SlowBlit(image, rect, capture_data);
+    SlowBlit(image, rect, frame);
   }
 }
 
-void ScreenCapturerLinux::FastBlit(uint8* image, const SkIRect& rect,
-                                   ScreenCaptureData* capture_data) {
+void ScreenCapturerLinux::FastBlit(uint8* image,
+                                   const webrtc::DesktopRect& rect,
+                                   webrtc::DesktopFrame* frame) {
   uint8* src_pos = image;
   int src_stride = x_server_pixel_buffer_.GetStride();
-  int dst_x = rect.fLeft, dst_y = rect.fTop;
+  int dst_x = rect.left(), dst_y = rect.top();
 
-  uint8* dst_pos = capture_data->data() + capture_data->stride() * dst_y;
-  dst_pos += dst_x * ScreenCaptureData::kBytesPerPixel;
+  uint8* dst_pos = frame->data() + frame->stride() * dst_y;
+  dst_pos += dst_x * webrtc::DesktopFrame::kBytesPerPixel;
 
   int height = rect.height();
-  int row_bytes = rect.width() * ScreenCaptureData::kBytesPerPixel;
+  int row_bytes = rect.width() * webrtc::DesktopFrame::kBytesPerPixel;
   for (int y = 0; y < height; ++y) {
     memcpy(dst_pos, src_pos, row_bytes);
     src_pos += src_stride;
-    dst_pos += capture_data->stride();
+    dst_pos += frame->stride();
   }
 }
 
-void ScreenCapturerLinux::SlowBlit(uint8* image, const SkIRect& rect,
-                                   ScreenCaptureData* capture_data) {
+void ScreenCapturerLinux::SlowBlit(uint8* image,
+                                   const webrtc::DesktopRect& rect,
+                                   webrtc::DesktopFrame* frame) {
   int src_stride = x_server_pixel_buffer_.GetStride();
-  int dst_x = rect.fLeft, dst_y = rect.fTop;
+  int dst_x = rect.left(), dst_y = rect.top();
   int width = rect.width(), height = rect.height();
 
   uint32 red_mask = x_server_pixel_buffer_.GetRedMask();
@@ -551,9 +532,9 @@ void ScreenCapturerLinux::SlowBlit(uint8* image, const SkIRect& rect,
 
   unsigned int bits_per_pixel = x_server_pixel_buffer_.GetBitsPerPixel();
 
-  uint8* dst_pos = capture_data->data() + capture_data->stride() * dst_y;
+  uint8* dst_pos = frame->data() + frame->stride() * dst_y;
   uint8* src_pos = image;
-  dst_pos += dst_x * ScreenCaptureData::kBytesPerPixel;
+  dst_pos += dst_x * webrtc::DesktopFrame::kBytesPerPixel;
   // TODO(hclam): Optimize, perhaps using MMX code or by converting to
   // YUV directly
   for (int y = 0; y < height; y++) {
@@ -577,7 +558,7 @@ void ScreenCapturerLinux::SlowBlit(uint8* image, const SkIRect& rect,
       dst_pos_32[x] = ((r >> 8) & 0xff0000) | ((g >> 16) & 0xff00) |
           ((b >> 24) & 0xff);
     }
-    dst_pos += capture_data->stride();
+    dst_pos += frame->stride();
     src_pos += src_stride;
   }
 }
@@ -609,15 +590,6 @@ uint32 ScreenCapturerLinux::GetRgbShift(uint32 mask) {
 
 }  // namespace
 
-scoped_refptr<SharedBuffer> ScreenCapturer::Delegate::CreateSharedBuffer(
-    uint32 size) {
-  return scoped_refptr<SharedBuffer>();
-}
-
-void ScreenCapturer::Delegate::ReleaseSharedBuffer(
-    scoped_refptr<SharedBuffer> buffer) {
-}
-
 // static
 scoped_ptr<ScreenCapturer> ScreenCapturer::Create() {
   scoped_ptr<ScreenCapturerLinux> capturer(new ScreenCapturerLinux());