scheduler: Disable expensive timers during main thread user input

components/scheduler/renderer/task_cost_estimator.cc

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "components/scheduler/renderer/task_cost_estimator.h"
+
+namespace scheduler {
+
+TaskCostEstimator::TaskCostEstimator(int sample_count,
+                                     double estimation_percentile)
+    : rolling_time_delta_history_(sample_count),
+      outstanding_task_count_(0),
+      estimation_percentile_(estimation_percentile) {}
+
+TaskCostEstimator::~TaskCostEstimator() {}
+
+void TaskCostEstimator::WillProcessTask(const base::PendingTask& pending_task) {
+  // Avoid measuring the duration in nested run loops.
+  if (++outstanding_task_count_ == 1)
+    task_start_time_ = base::TimeTicks::Now();
+}
+
+void TaskCostEstimator::DidProcessTask(const base::PendingTask& pending_task) {
+  if (--outstanding_task_count_ == 0) {
+    base::TimeDelta duration = base::TimeTicks::Now() - task_start_time_;
+    rolling_time_delta_history_.InsertSample(duration);
+
+    // TODO(skyostil): Should we do this less often?

[alex clarke (OOO till 29th), 2015/08/21 17:13:30]

I doubt it's terribly expensive.

[Sami, 2015/08/21 17:42:22]

Yeah, let's see if it shows up in any profiles.

+    expected_task_duration_ =
+        rolling_time_delta_history_.Percentile(estimation_percentile_);
+  }
+}
+
+}  // namespace scheduler