ContentCapture: Add dedicated TraceEvent

This patch added content-capture trace event category, also traced
scheduling task and task running event.

Bug: 1006418
Change-Id: I2dbe38bbf3e09645abb6185e8efa15587ffb00ec
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1817282Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
Reviewed-by: Sami Kyöstilä <skyostil@chromium.org>
Commit-Queue: Tao Bai <michaelbai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#699899}

base/trace_event/builtin_categories.h

@@ -52,6 +52,7 @@
   X("cma")                                                               \
   X("compositor")                                                        \
   X("content")                                                           \
+  X("content-capture")                                                   \
   X("devtools")                                                          \
   X("devtools.timeline")                                                 \
   X("devtools.timeline.async")                                           \

third_party/blink/renderer/core/content_capture/content_capture_task.cc

@@ -196,7 +196,7 @@ bool ContentCaptureTask::RunInternal() {
 }
 
 void ContentCaptureTask::Run(TimerBase*) {
-  TRACE_EVENT0("blink", "CaptureContentTask::Run");
+  TRACE_EVENT0("content-capture", "RunTask");
   is_scheduled_ = false;
   if (!RunInternal()) {
     ScheduleInternal(ScheduleReason::kRetryTask);
@@ -229,6 +229,8 @@ void ContentCaptureTask::ScheduleInternal(ScheduleReason reason) {
 
   delay_task_->StartOneShot(delay, FROM_HERE);
   is_scheduled_ = true;
+  TRACE_EVENT_INSTANT1("content-capture", "ScheduleTask",
+                       TRACE_EVENT_SCOPE_THREAD, "reason", reason);
 }
 
 void ContentCaptureTask::Schedule(ScheduleReason reason) {