media: avoid crash when VCD client fails to get I420 output buffer

We should discard the incoming capture GpuMemoryBuffer and return when
VideoCaptureDeviceClient::OnIncomingCapturedGfxBuffer fails to reserve
the I420 output buffer. Otherwise we'll end up crashing.

BUG=b:79729317
R=emircan

Change-Id: I616d97ca618ad9cc40abdf9d1a8f06ce568cfbb0
Reviewed-on: https://chromium-review.googlesource.com/1059495Reviewed-by: Emircan Uysaler <emircan@chromium.org>
Commit-Queue: Ricky Liang <jcliang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#558721}

media/capture/video/video_capture_device_client.cc

@@ -333,6 +333,10 @@ void VideoCaptureDeviceClient::OnIncomingCapturedGfxBuffer(
   auto output_buffer =
       ReserveOutputBuffer(dimensions, PIXEL_FORMAT_I420, frame_feedback_id);
 
+  // Failed to reserve I420 output buffer, so drop the frame.
+  if (!output_buffer.is_valid())
+    return;
+
   uint8_t* y_plane_data;
   uint8_t* u_plane_data;
   uint8_t* v_plane_data;