Add trace events to debug sampling profiler issue with slow-reports

There are strange behaviors observed in the field with the sampling
profiler. It seems there are two running sampling profiler but only
one is reporting events.

This CL is adding trace events to help investigate this problem.

R=wittman@chromium.org

Bug: 882982
Change-Id: I70925e841b8a1f0e47564350d142f056d8b8ae99
Reviewed-on: https://chromium-review.googlesource.com/c/1302318Reviewed-by: Mike Wittman <wittman@chromium.org>
Commit-Queue: Etienne Bergeron <etienneb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#603235}

base/profiler/stack_sampling_profiler.cc

@@ -24,6 +24,7 @@
 #include "base/threading/thread_restrictions.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "base/timer/elapsed_timer.h"
+#include "base/trace_event/trace_event.h"
 
 namespace base {
 
@@ -443,6 +444,9 @@ void StackSamplingProfiler::SamplingThread::ScheduleShutdownIfIdle() {
   if (!active_collections_.empty())
     return;
 
+  TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("cpu_profiler"),
+               "StackSamplingProfiler::SamplingThread::ScheduleShutdownIfIdle");
+
   int add_events;
   {
     AutoLock lock(thread_execution_state_lock_);
@@ -559,6 +563,9 @@ void StackSamplingProfiler::SamplingThread::ShutdownTask(int add_events) {
   if (thread_execution_state_add_events_ != add_events)
     return;
 
+  TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("cpu_profiler"),
+               "StackSamplingProfiler::SamplingThread::ShutdownTask");
+
   // There can be no new AddCollectionTasks at this point because creating
   // those always increments "add events". There may be other requests, like
   // Remove, but it's okay to schedule the thread to stop once they've been
@@ -650,10 +657,15 @@ StackSamplingProfiler::StackSamplingProfiler(
       profiling_inactive_(kResetPolicy, WaitableEvent::InitialState::SIGNALED),
       profiler_id_(kNullProfilerId),
       test_delegate_(test_delegate) {
+  TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("cpu_profiler"),
+               "StackSamplingProfiler::StackSamplingProfiler");
   DCHECK(profile_builder_);
 }
 
 StackSamplingProfiler::~StackSamplingProfiler() {
+  TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("cpu_profiler"),
+               "StackSamplingProfiler::~StackSamplingProfiler");
+
   // Stop returns immediately but the shutdown runs asynchronously. There is a
   // non-zero probability that one more sample will be taken after this call
   // returns.
@@ -673,6 +685,9 @@ StackSamplingProfiler::~StackSamplingProfiler() {
 }
 
 void StackSamplingProfiler::Start() {
+  TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("cpu_profiler"),
+               "StackSamplingProfiler::Start");
+
   // Multiple calls to Start() for a single StackSamplingProfiler object is not
   // allowed. If profile_builder_ is nullptr, then Start() has been called
   // already.
@@ -702,9 +717,15 @@ void StackSamplingProfiler::Start() {
           thread_id_, params_, &profiling_inactive_, std::move(native_sampler_),
           std::move(profile_builder_)));
   DCHECK_NE(kNullProfilerId, profiler_id_);
+
+  TRACE_EVENT1(TRACE_DISABLED_BY_DEFAULT("cpu_profiler"),
+               "StackSamplingProfiler::Started", "profiler_id", profiler_id_);
 }
 
 void StackSamplingProfiler::Stop() {
+  TRACE_EVENT1(TRACE_DISABLED_BY_DEFAULT("cpu_profiler"),
+               "StackSamplingProfiler::Stop", "profiler_id", profiler_id_);
+
   SamplingThread::GetInstance()->Remove(profiler_id_);
   profiler_id_ = kNullProfilerId;
 }