wip experimentation with AVCaptureDepthData in webrtc

AVCaptureDepthDataOutput.patch

diff --git a/sdk/objc/Framework/Classes/Video/RTCAVFoundationVideoCapturerInternal.h b/sdk/objc/Framework/Classes/Video/RTCAVFoundationVideoCapturerInternal.h
index 8b73a8086..6b23e8a81 100644
--- a/sdk/objc/Framework/Classes/Video/RTCAVFoundationVideoCapturerInternal.h
+++ b/sdk/objc/Framework/Classes/Video/RTCAVFoundationVideoCapturerInternal.h
@@ -24,6 +24,9 @@ NS_ASSUME_NONNULL_BEGIN
 @interface RTCAVFoundationVideoCapturerInternal
     : NSObject <AVCaptureVideoDataOutputSampleBufferDelegate>
 
+@interface RTCAVFoundationVideoCapturerInternal
+    : NSObject <AVCaptureDepthDataOutputDelegate>
+
 @property(nonatomic, readonly) AVCaptureSession *captureSession;
 @property(nonatomic, readonly) dispatch_queue_t frameQueue;
 @property(nonatomic, readonly) BOOL canUseBackCamera;
diff --git a/sdk/objc/Framework/Classes/Video/RTCAVFoundationVideoCapturerInternal.mm b/sdk/objc/Framework/Classes/Video/RTCAVFoundationVideoCapturerInternal.mm
index 287ecdd71..b9cc14814 100644
--- a/sdk/objc/Framework/Classes/Video/RTCAVFoundationVideoCapturerInternal.mm
+++ b/sdk/objc/Framework/Classes/Video/RTCAVFoundationVideoCapturerInternal.mm
@@ -263,6 +263,61 @@
   RTCLogError(@"Dropped sample buffer.");
 }
 
+#pragma mark AVCaptureDepthDataOutputDelegate
+
+- (void)depthDataOutput:(AVCaptureDepthDataOutput *)depthDataOutput
+              didOutput:(AVDepthData *)depthData
+              timestamp:(CMTime)timestamp 
+             connection:(AVCaptureConnection *)connection {
+
+  // FIXME: should we track our AVCaptureDepthDataOutput like we track our 
+  // AVCaptureDepthDataOutput               
+  // NSParameterAssert(depthDataOutput == _videoDataOutput);
+
+  if (!self.hasStarted) {
+    return;
+  }
+
+  // Assume that rotation metadata, if any, will be tracked by non-depth capture
+  // where we can use AVCaptureSession devicePositionForSampleBuffer correctly
+  webrtc::VideoRotation rotation = webrtc::kVideoRotation_0;
+
+  OSStatus status;
+  CMFormatDescriptionRef desc = NULL;
+  status = CMVideoFormatDescriptionCreateForImageBuffer(NULL, depthData->depthDataMap, &desc);
+  if (status != noErr) {
+    RTC_LOG(LS_ERROR) << "CMVideoFormatDescriptionCreateForImageBuffer failed to set: " << status;
+  }
+
+  CMSampleTimingInfo timing;
+  timing.duration = kCMTimeInvalid;
+  timing.presentationTimeStamp = timestamp;
+  timing.decodeTimeStamp = kCMTimeInvalid;
+
+  // Convert our depthData into a SampleBuffer
+  CMSampleBufferRef sampleBuffer;
+  status = CMSampleBufferCreateReadyWithImageBuffer(
+    kCFAllocatorDefault,
+    depthData->depthDataMap,
+    desc,
+    &timing,
+    &sampleBuffer
+  );
+  if (status != noErr) {
+    RTC_LOG(LS_ERROR) << "CMSampleBufferCreateReadyWithImageBuffer failed to set: " << status;
+  }
+
+  _capturer->CaptureSampleBuffer(sampleBuffer, rotation);
+}
+
+- (void)depthDataOutput:(AVCaptureDepthDataOutput *)output 
+       didDropDepthData:(AVDepthData *)depthData 
+              timestamp:(CMTime)timestamp 
+             connection:(AVCaptureConnection *)connection 
+                 reason:(AVCaptureOutputDataDroppedReason)reason {
+  RTCLogError(@"Dropped depthData buffer.");
+}
+
 #pragma mark - AVCaptureSession notifications
 
 - (void)handleCaptureSessionInterruption:(NSNotification *)notification {