Add a ChromeOS implementation of VideoCaptureDevice

media/video/capture/linux/video_capture_device_chromeos.cc

+// Copyright 2014 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.
+
+#include "media/video/capture/linux/video_capture_device_chromeos.h"
+
+#include "base/bind.h"
+#include "base/memory/ref_counted.h"
+#include "ui/gfx/display.h"
+#include "ui/gfx/screen.h"
+
+namespace media {
+
+// This is a delegate class used to transfer Display change events from the UI
+// thread to the media thread.
+class VideoCaptureDeviceChromeOS::ScreenObserverDelegate
+    : public gfx::DisplayObserver,
+      public base::RefCountedThreadSafe<ScreenObserverDelegate> {
+ public:
+  ScreenObserverDelegate(VideoCaptureDeviceChromeOS* capture_device)
+      : capture_device_(capture_device),
+        media_message_loop_(base::MessageLoop::current()) {
+    base::MessageLoopForUI::current()->PostTask(
+      FROM_HERE,
+      base::Bind(&ScreenObserverDelegate::AddObserverOnUIThread, this));
+  }
+
+  ~ScreenObserverDelegate() {
+    DCHECK(!capture_device_);
+  }
+
+  void RemoveObserver() {
+    capture_device_ = NULL;
+    base::MessageLoopForUI::current()->PostTask(
+      FROM_HERE,
+      base::Bind(&ScreenObserverDelegate::RemoveObserverOnUIThread, this));
+  }
+
+ private:
+  friend class base::RefCountedThreadSafe<ScreenObserverDelegate>;

[mcasas, 2014/05/11 18:41:25]

According to base/memory/ref_counted.h, if you use the 
friend idiom the destructor should be private. Does it 
apply here?

[Zachary Kuznia, 2014/05/12 02:54:18]

Done.

+
+  // gfx::DisplayObserver:
+  virtual void OnDisplayBoundsChanged(const gfx::Display& display) OVERRIDE {
+    SendDisplayRotation(display);
+  }
+
+  virtual void OnDisplayAdded(const gfx::Display& /*new_display*/) OVERRIDE {}
+  virtual void OnDisplayRemoved(const gfx::Display& /*old_display*/) OVERRIDE {}

[mcasas, 2014/05/11 18:41:25]

Shouldn't these 3 methods from gfx::DisplayObserver be public?

[Zachary Kuznia, 2014/05/12 02:54:18]

This is a controversial topic.  See:
https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/CwzjcWd9cYM

I prefer keeping them private, personally, but I'm more than happy to follow
whichever convention is preferred by you.

+
+  void AddObserverOnUIThread() {
+    gfx::Screen* screen =
+        gfx::Screen::GetScreenByType(gfx::SCREEN_TYPE_ALTERNATE);

[mcasas, 2014/05/11 18:41:25]

Why not gfx::SCREEN_TYPE_NATIVE?

[Zachary Kuznia, 2014/05/12 02:54:18]

Because this is the pattern established in ash/shell.cc.  They're only different
on Windows, so either would work.  As such, following ash seems best.

+    if (screen) {
+      screen->AddObserver(this);
+      SendDisplayRotation(screen->GetPrimaryDisplay());
+    }
+  }
+
+  void RemoveObserverOnUIThread() {
+    gfx::Screen* screen =
+        gfx::Screen::GetScreenByType(gfx::SCREEN_TYPE_ALTERNATE);
+    if (screen)
+      screen->RemoveObserver(this);
+  }
+
+  void SendDisplayRotation(const gfx::Display& display) {
+    media_message_loop_->PostTask(
+      FROM_HERE,
+      base::Bind(&ScreenObserverDelegate::SendDisplayRotationOnMediaThread,
+                 this, display));
+  }
+
+  void SendDisplayRotationOnMediaThread(const gfx::Display& display) {
+    capture_device_->SetDisplayRotation(display);
+  }
+
+  VideoCaptureDeviceChromeOS* capture_device_;

[mcasas, 2014/05/11 18:41:25]

Ugh naked pointer. Maybe const?

[Zachary Kuznia, 2014/05/12 02:54:18]

Unfortunately, that would require marking rotation_ as mutable in
VideoCaptureDeviceLinux.

+  base::MessageLoop* media_message_loop_;

[mcasas, 2014/05/11 18:41:25]

const?

ultra-nit: would you mind terribly calling it |capture_thread_loop_|?
And changing "Media" -> "Capture".

[Zachary Kuznia, 2014/05/12 02:54:18]

Nits Done.  The MessageLoop pointer can't be const, as PostTask is not const.

+  DISALLOW_IMPLICIT_CONSTRUCTORS(ScreenObserverDelegate);
+};
+
+
+VideoCaptureDeviceChromeOS::VideoCaptureDeviceChromeOS(const Name& device_name)
+    : VideoCaptureDeviceLinux(device_name),
+      screen_observer_delegate_(new ScreenObserverDelegate(this)) {
+}
+
+VideoCaptureDeviceChromeOS::~VideoCaptureDeviceChromeOS() {
+

[mcasas, 2014/05/11 18:41:25]

nit: no empty line.

[Zachary Kuznia, 2014/05/12 02:54:18]

Done.

+}
+
+void VideoCaptureDeviceChromeOS::SetDisplayRotation(
+    const gfx::Display& display) {
+  if (display.IsInternal())
+    SetRotation(display.rotation() * 90);
+}
+
+}  // namespace media