VideoCapture: more migration IPC-->mojo, part 6

content/common/video_capture.mojom

Index: content/common/video_capture.mojom
diff --git a/content/common/video_capture.mojom b/content/common/video_capture.mojom
index 672b720fbdc95dafb6da75bc2dc1994601cb630b..b7e200702de08c963387b1142aa5d449b74d45c1 100644
--- a/content/common/video_capture.mojom
+++ b/content/common/video_capture.mojom
@@ -11,6 +11,47 @@ import "services/video_capture/public/interfaces/video_capture_device_proxy.mojo
 import "services/video_capture/public/interfaces/video_capture_format.mojom";
 import "ui/gfx/geometry/mojo/geometry.mojom";
 
+// This file decribes the communication between a given Renderer Host interface
+// implementation (VideoCaptureHost) and a remote VideoCaptureObserver.
+// VideoCaptureHost offers a stateless part (GetDeviceSupportedFormats() and
+// GetDeviceFormatsInUse()) that can be invoked at any time, and a stateful part
+// sandwiched between Start() and Stop(). A Client's OnStateChanged() can be
+// notified any time during the stateful part. The stateful part is composed of
+// a preamble where a Renderer client sends a command to Start() the capture,
+// registering itself as the associated remote VideoCaptureObserver. The Host
+// will then create and pre- share a number of buffers:
+//
+//   Observer                                        VideoCaptureHost
+//      | ---> StartCapture                                     |
+//      |                        OnStateChanged(STARTED) <---   |
+//      |                             OnBufferCreated(1) <---   |
+//      |                             OnBufferCreated(2) <---   |
+//      =                                                       =
+// and capture will then refer to those preallocated buffers:
+//      |                               OnBufferReady(1) <---   |
+//      |                               OnBufferReady(2) <---   |
+//      | ---> ReleaseBuffer(1)                                 |
+//      |                               OnBufferReady(1) <---   |
+//      | ---> ReleaseBuffer(2)                                 |
+//      |                               OnBufferReady(2) <---   |
+//      | ---> ReleaseBuffer(1)                                 |
+//      |                         ...                           |
+//      =                                                       =
+// Buffers can be reallocated with a larger size, if e.g. resolution changes.
+//      |                 (resolution change)                   |
+//      |                           OnBufferDestroyed(1) <---   |
+//      |                             OnBufferCreated(3) <---   |
+//      |                               OnBufferReady(3) <---   |
+//      | ---> ReleaseBuffer(2)                                 |
+//      |                           OnBufferDestroyed(2) <---   |
+//      |                             OnBufferCreated(5) <---   |
+//      |                               OnBufferReady(5) <---   |
+//      =                                                       =
+// In the communication epilogue, the client Stop()s capture, receiving a last
+// status update:
+//      | ---> StopCapture                                      |
+//      |                        OnStateChanged(STOPPED) <---   |
+
 struct VideoCaptureParams {
   video_capture.mojom.VideoCaptureFormat requested_format;
   video_capture.mojom.ResolutionChangePolicy resolution_change_policy;
@@ -41,14 +82,15 @@ interface VideoCaptureObserver {
   // Gets notified about a VideoCaptureState update.
   OnStateChanged(VideoCaptureState state);
 
+  // A new buffer identified by |buffer_id| has been created for video capture.
+  OnBufferCreated(int32 buffer_id, handle<shared_buffer> handle_fd);
+
   // |buffer_id| has video capture data with |info| containing the associated
   // VideoFrame constituent parts.
   OnBufferReady(int32 buffer_id, VideoFrameInfo info);
 
   // |buffer_id| has been released by VideoCaptureHost and must not be used.
   OnBufferDestroyed(int32 buffer_id);
-
-  // TODO(mcasas): Migrate the rest of the messages, https://crbug.com/651897.
 };
 
 interface VideoCaptureHost {