Revert of [Mojo Video Capture] Simplify media::VideoCaptureDevice::Client:Buffer to a struct

media/capture/video/video_capture_buffer_pool_impl.cc

Index: media/capture/video/video_capture_buffer_pool_impl.cc
diff --git a/media/capture/video/video_capture_buffer_pool_impl.cc b/media/capture/video/video_capture_buffer_pool_impl.cc
index d833f008ca3890a5deb7c3968040b5104e83f09d..7bc10e16e9e2b4bcd2f18b186e64c5d3ad3cfc48 100644
--- a/media/capture/video/video_capture_buffer_pool_impl.cc
+++ b/media/capture/video/video_capture_buffer_pool_impl.cc
@@ -27,8 +27,8 @@
 
 VideoCaptureBufferPoolImpl::~VideoCaptureBufferPoolImpl() {}
 
-mojo::ScopedSharedBufferHandle
-VideoCaptureBufferPoolImpl::GetHandleForInterProcessTransit(int buffer_id) {
+mojo::ScopedSharedBufferHandle VideoCaptureBufferPoolImpl::GetHandleForTransit(
+    int buffer_id) {
   base::AutoLock lock(lock_);
 
   VideoCaptureBufferTracker* tracker = GetTracker(buffer_id);
@@ -40,16 +40,17 @@
 }
 
 std::unique_ptr<VideoCaptureBufferHandle>
-VideoCaptureBufferPoolImpl::GetHandleForInProcessAccess(int buffer_id) {
-  base::AutoLock lock(lock_);
-
-  VideoCaptureBufferTracker* tracker = GetTracker(buffer_id);
-  if (!tracker) {
-    NOTREACHED() << "Invalid buffer_id.";
-    return nullptr;
-  }
-
-  return tracker->GetMemoryMappedAccess();
+VideoCaptureBufferPoolImpl::GetBufferHandle(int buffer_id) {
+  base::AutoLock lock(lock_);
+
+  VideoCaptureBufferTracker* tracker = GetTracker(buffer_id);
+  if (!tracker) {
+    NOTREACHED() << "Invalid buffer_id.";
+    return std::unique_ptr<VideoCaptureBufferHandle>();
+  }
+
+  DCHECK(tracker->held_by_producer());
+  return tracker->GetBufferHandle();
 }
 
 int VideoCaptureBufferPoolImpl::ReserveForProducer(