media/gpu/vaapi: Add TRACE for Decode() call

The new direct Vaapi VideoDecoder doesn't have tracing, this CL adds the
first such meas, for the Decode() call, similar to
https://source.chromium.org/chromium/chromium/src/+/master:media/gpu/vaapi/vaapi_video_decode_accelerator.cc;l=446

Bug: 1040291
Change-Id: I25b70cecb48435cd5539cbf927c0f2547d584649
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2283249
Auto-Submit: Miguel Casas <mcasas@chromium.org>
Reviewed-by: Miguel Casas <mcasas@chromium.org>
Reviewed-by: Hirokazu Honda <hiroh@chromium.org>
Commit-Queue: Hirokazu Honda <hiroh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#785864}

media/gpu/vaapi/vaapi_video_decoder.cc

@@ -10,6 +10,7 @@
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/memory/ptr_util.h"
+#include "base/trace_event/trace_event.h"
 #include "media/base/bind_to_current_loop.h"
 #include "media/base/format_utils.h"
 #include "media/base/video_frame.h"
@@ -222,7 +223,9 @@ void VaapiVideoDecoder::HandleDecodeTask() {
     return;
   }
 
+  TRACE_EVENT_BEGIN0("media,gpu", "VaapiVideoDecoder::Decode");
   AcceleratedVideoDecoder::DecodeResult decode_result = decoder_->Decode();
+  TRACE_EVENT_END0("media,gpu", "VaapiVideoDecoder::Decode");
   switch (decode_result) {
     case AcceleratedVideoDecoder::kRanOutOfStreamData:
       // Decoding was successful, notify client and try to schedule the next