Update TabCapturePerformanceTest to more accurately time captures.

content/browser/media/capture/content_video_capture_device_core.cc

Index: content/browser/media/capture/content_video_capture_device_core.cc
diff --git a/content/browser/media/capture/content_video_capture_device_core.cc b/content/browser/media/capture/content_video_capture_device_core.cc
index 403e8a67b391bc9d9e8e0a7eaa736a6d681bda35..f242d6b5296be88b55924f35a27841f9502f68a1 100644
--- a/content/browser/media/capture/content_video_capture_device_core.cc
+++ b/content/browser/media/capture/content_video_capture_device_core.cc
@@ -182,6 +182,9 @@ void ThreadSafeCaptureOracle::DidCaptureFrame(
 
   if (success) {
     if (oracle_.CompleteCapture(frame_number, &timestamp)) {
+      TRACE_EVENT_INSTANT0("gpu.capture", "CaptureSucceeded",
+                           TRACE_EVENT_SCOPE_THREAD);
+
       frame->metadata()->SetDouble(media::VideoFrameMetadata::FRAME_RATE,
                                    params_.requested_format.frame_rate);
       frame->metadata()->SetTimeTicks(