media/gpu/v4l2ip: use buffer affinity tracker

When using DMABUFs, it is preferable to use the same V4L2 buffer with
the same underlying buffer, as failure to do so results in memory
unmappings/remappings in the driver. Use the newly introduced buffer
affinity tracker and V4L2Queue::GetFreeBufferForFrame() method to
achieve this transparently in the image processor.

BUG=b:159688625
TEST=video.DecodeAccel.h264 passes on Kukui.

Change-Id: I9df69431d0e532c40c0f49ca4e3bb31843b0814b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2413946
Commit-Queue: Alexandre Courbot <acourbot@chromium.org>
Reviewed-by: Fritz Koenig <frkoenig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#813091}

media/gpu/v4l2/v4l2_image_processor_backend.cc

@@ -613,8 +613,26 @@ void V4L2ImageProcessorBackend::ProcessJobsTask() {
     }
 
     // We need one input and one output buffer to schedule the job
-    auto input_buffer = input_queue_->GetFreeBuffer();
-    auto output_buffer = output_queue_->GetFreeBuffer();
+    base::Optional<V4L2WritableBufferRef> input_buffer;
+    // If we are using DMABUF frames, try to always obtain the same V4L2 buffer.
+    if (input_memory_type_ == V4L2_MEMORY_DMABUF) {
+      const VideoFrame& input_frame =
+          *(input_job_queue_.front()->input_frame.get());
+      input_buffer = input_queue_->GetFreeBufferForFrame(input_frame);
+    }
+    if (!input_buffer)
+      input_buffer = input_queue_->GetFreeBuffer();
+
+    base::Optional<V4L2WritableBufferRef> output_buffer;
+    // If we are using DMABUF frames, try to always obtain the same V4L2 buffer.
+    if (output_memory_type_ == V4L2_MEMORY_DMABUF) {
+      const VideoFrame& output_frame =
+          *(input_job_queue_.front()->output_frame.get());
+      output_buffer = output_queue_->GetFreeBufferForFrame(output_frame);
+    }
+    if (!output_buffer)
+      output_buffer = output_queue_->GetFreeBuffer();
+
     if (!input_buffer || !output_buffer)
       break;