Add still image capture interface for VideoCaptureDevice.

media/video/capture/video_capture_device.h

Index: media/video/capture/video_capture_device.h
diff --git a/media/video/capture/video_capture_device.h b/media/video/capture/video_capture_device.h
index 382dad6cdc461d7d6d20bf04ab8e7e91693ae503..614fc08aea8ce680a0a7c71014eaf1105a64b2ae 100644
--- a/media/video/capture/video_capture_device.h
+++ b/media/video/capture/video_capture_device.h
@@ -216,6 +216,33 @@ class MEDIA_EXPORT VideoCaptureDevice {
 
     // VideoCaptureDevice requests the |message| to be logged.
     virtual void OnLog(const std::string& message) {}
+
+    // The video stream has been muted. After this callback, no more
+    // OnIncomingCapturedData() will be called. This may happen when
+    // CaptureImage() has called. After the still image has been captured, the
+    // client will get notified by OnUnmute() and the video stream will be
+    // resumed.
+    virtual void OnMute() {}
+
+    // The video stream has resumed.
+    virtual void OnUnmute() {}
+  };
+
+  class MEDIA_EXPORT ImageClient {
+   public:
+    virtual ~ImageClient() {}
+
+    // Callback function to notify the client the caputred image is available.
+    virtual void OnIncomingCapturedData(const uint8* data,
+                                        int length,
+                                        const ImageCaptureFormat& format,
+                                        int rotation,
+                                        base::TimeTicks timestamp) = 0;
+
+    // Callback function to notify client the failure of the image capturing.

[wuchengli, 2014/09/15 06:14:13]

s/capturing/capture/

[Owen Lin, 2014/09/15 09:04:36]

Done.

+    // The VideoCaptureDevice must be StopAndDeAllocate()-ed. |reason| is a
+    // text description of the error.
+    virtual void OnError(const std::string& reason) = 0;

[wuchengli, 2014/09/15 06:14:13]

We want an integer error to report to the error callback of pepper api. Change
string to int or enum.

[Owen Lin, 2014/09/15 09:04:36]

Can we keep it for consistency ? We are still far from the PPAPI. I think all of
the errors here could be aggregated as one error in the PPAPI, e.g.
PLATFORM_ERROR?

[Owen Lin, 2014/09/16 02:35:15]

The current errors are

1. Fail to open the device
2. The opened device doesn't support video capture
3. No supported format found on the device. 
4. IOCTL fail: S_FMT, S_PARM, VIDIOC_STREAMON, VIDIOC_STREAMOFF, VIDIOC_QBUF,
VIDIOC_REQBUFS, VIDIOC_QUERYBUF ....
5. Timeout on waiting a frame.

All the errors are not expected. Once happen, the device is in an error state.
Need to restart the device to recover. 
On 2014/09/15 09:04:36, Owen Lin wrote:

   };
 
   // Creates a VideoCaptureDevice object.
@@ -235,6 +262,12 @@ class MEDIA_EXPORT VideoCaptureDevice {
   static void GetDeviceSupportedFormats(const Name& device,
                                         VideoCaptureFormats* supported_formats);
 
+  // Gets the supported formats for still image of a particular device attached
+  // to the system.
+  static void GetDeviceSupportedImageFormats(
+      const Name& device,
+      ImageCaptureFormats* supported_formats);
+
   // Prepares the camera for use. After this function has been called no other
   // applications can use the camera. StopAndDeAllocate() must be called before
   // the object is deleted.
@@ -258,6 +291,30 @@ class MEDIA_EXPORT VideoCaptureDevice {
   // defined, otherwise returns 0.
   int GetPowerLineFrequencyForLocation() const;
 
+  // Initializes the device for still image capture for the given image format.
+  //
+  // This function must be called between AllocateAndStart() and
+  // StopAndDeAllocate().
+  virtual void InitializeImageCapture(const ImageCaptureFormat& image_format,
+                                      scoped_ptr<ImageClient> client) {}
+
+  // Releases resources for image capture.
+  //
+  // The ImageClient passed from InitializeImageCapture would be freed. This
+  // method must be called between InitializeImageCapture() and
+  // StopAndDeAllocate().
+  virtual void ReleaseImageCapture() {}
+
+  // Gets one image from the device asynchronously.
+  //
+  // It will return the image by the ImageClient::OnIncomingCapturedData()
+  // callback. If the video stream has to be stopped to capture the still image,
+  // the Client::OnMute() and Client::OnUnmute() will be called.
+  //
+  // This function must be called between InitializeImageCapture() and
+  // ReleaseImageCapture().
+  virtual void CaptureImage() {}
+
  protected:
   static const int kPowerLine50Hz = 50;
   static const int kPowerLine60Hz = 60;