Move and rename TaskTimeTracker to public interface exposed to WebThread, use in WebPerf Agent.

third_party/WebKit/Source/platform/scheduler/base/task_queue_manager.cc

Index: third_party/WebKit/Source/platform/scheduler/base/task_queue_manager.cc
diff --git a/third_party/WebKit/Source/platform/scheduler/base/task_queue_manager.cc b/third_party/WebKit/Source/platform/scheduler/base/task_queue_manager.cc
index 31adb7257af790faa8ed72b0ed0487afd98a3768..ca32dd893eefe3c966d0a01ca7e45ccb447c4588 100644
--- a/third_party/WebKit/Source/platform/scheduler/base/task_queue_manager.cc
+++ b/third_party/WebKit/Source/platform/scheduler/base/task_queue_manager.cc
@@ -14,9 +14,9 @@
 #include "platform/scheduler/base/task_queue_impl.h"
 #include "platform/scheduler/base/task_queue_manager_delegate.h"
 #include "platform/scheduler/base/task_queue_selector.h"
-#include "platform/scheduler/base/task_time_tracker.h"
 #include "platform/scheduler/base/work_queue.h"
 #include "platform/scheduler/base/work_queue_sets.h"
+#include "public/platform/scheduler/base/task_time_tracker.h"
 
 namespace blink {
 namespace scheduler {
@@ -34,6 +34,11 @@ void RecordImmediateTaskQueueingDuration(tracked_objects::Duration duration) {
       "RendererScheduler.TaskQueueManager.ImmediateTaskQueueingDuration",
       base::TimeDelta::FromMilliseconds(duration.InMilliseconds()));
 }
+
+double MonotonicTimeInSeconds(base::TimeTicks timeTicks) {
+  return (timeTicks.ToInternalValue() /

[alph, 2016/08/22 23:51:07]

nit: (timeTicks - base::TimeTicks()).InSecondsF()

[panicker, 2016/08/25 23:11:52]

Done.

+          static_cast<double>(base::Time::kMicrosecondsPerSecond));
+}
 }
 
 TaskQueueManager::TaskQueueManager(
@@ -46,7 +51,6 @@ TaskQueueManager::TaskQueueManager(
       task_was_run_on_quiescence_monitored_queue_(false),
       work_batch_size_(1),
       task_count_(0),
-      task_time_tracker_(nullptr),
       tracing_category_(tracing_category),
       disabled_by_default_tracing_category_(
           disabled_by_default_tracing_category),
@@ -197,7 +201,7 @@ void TaskQueueManager::DoWork(base::TimeTicks run_time, bool from_main_thread) {
   LazyNow lazy_now(real_time_domain()->CreateLazyNow());
   base::TimeTicks task_start_time;
 
-  if (!delegate_->IsNested() && task_time_tracker_)
+  if (!delegate_->IsNested() && task_time_trackers_.might_have_observers())
     task_start_time = lazy_now.Now();
 
   // Pass false and nullptr to UpdateWorkQueues here to prevent waking up a
@@ -228,10 +232,12 @@ void TaskQueueManager::DoWork(base::TimeTicks run_time, bool from_main_thread) {
     }
 
     lazy_now = real_time_domain()->CreateLazyNow();
-    if (!delegate_->IsNested() && task_time_tracker_) {
+    if (!delegate_->IsNested() && task_time_trackers_.might_have_observers()) {
       // Only report top level task durations.
       base::TimeTicks task_end_time = lazy_now.Now();
-      task_time_tracker_->ReportTaskTime(task_start_time, task_end_time);
+      FOR_EACH_OBSERVER(TaskTimeTracker, task_time_trackers_,
+                        ReportTaskTime(MonotonicTimeInSeconds(task_start_time),
+                                       MonotonicTimeInSeconds(task_end_time)));
       task_start_time = task_end_time;

[alph, 2016/08/22 23:51:07]

Looks like the first time the observer will get a bogus times. The
task_start_time is not initialized as there were no observers in the beginning.

[panickercorp, 2016/08/23 17:43:31]

There can be an issue if there are 0 observers at line 204 and an observer is
added before line 235.
In practice I don't think it's an issue as the renderer-scheduler is registered
as observer early on in its constructor. UNLESS the WorkerScheduler is created
beforehand and already processing tasks when the renderer-scheduler is created.

To be safe I could initialize task_start_time to base::TimeTicks() and add an
additional check here task_start_time != base::TimeTicks() (appears to be a
common pattern for checking validity of TimeTicks)

OTOH if this is not strictly necessary it could be needless overhead to do this
check per task. So maybe a comment instead?
Sami - any suggestions?

[panicker, 2016/08/25 23:11:52]

I'm leaving this as is, as this is not worse than today i.e. in theory
task_time_tracker_ could change from null to non-null between the 2 checks.

[Sami, 2016/08/26 11:03:56]

Sorry, I missed this question earlier. I think it would make sense to replace
the second might_have_observers() check with task_start_time ==
base::TimeTicks() check. It's not an error to call FOR_EACH_OBSERVER when there
are no observers. This would mean the clients don't need to guard against bogus
values.

     }
 
@@ -374,6 +380,17 @@ void TaskQueueManager::RemoveTaskObserver(
   task_observers_.RemoveObserver(task_observer);
 }
 
+void TaskQueueManager::AddTaskTimeTracker(TaskTimeTracker* task_time_tracker) {
+  DCHECK(main_thread_checker_.CalledOnValidThread());
+  task_time_trackers_.AddObserver(task_time_tracker);
+}
+
+void TaskQueueManager::RemoveTaskTimeTracker(
+    TaskTimeTracker* task_time_tracker) {
+  DCHECK(main_thread_checker_.CalledOnValidThread());
+  task_time_trackers_.RemoveObserver(task_time_tracker);
+}
+
 bool TaskQueueManager::GetAndClearSystemIsQuiescentBit() {
   bool task_was_run = task_was_run_on_quiescence_monitored_queue_;
   task_was_run_on_quiescence_monitored_queue_ = false;