Fix include

This translation unit is using THREAD_CHECKER but not including the
header.

Change-Id: Ifb594fe48ef0e9b08f80b3fc9898325f5c0d4f95
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1725644
Auto-Submit: Carlos Caballero <carlscab@google.com>
Commit-Queue: Hirokazu Honda <hiroh@chromium.org>
Reviewed-by: Hirokazu Honda <hiroh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#682558}

components/arc/video_accelerator/protected_buffer_manager.cc

@@ -11,6 +11,7 @@
 #include "base/logging.h"
 #include "base/memory/shared_memory.h"
 #include "base/system/sys_info.h"
+#include "base/threading/thread_checker.h"
 #include "components/arc/video_accelerator/protected_buffer_allocator.h"
 #include "media/gpu/macros.h"
 #include "mojo/public/cpp/system/buffer.h"