scheduler: Disable expensive timers during main thread user input

components/scheduler/renderer/task_cost_estimator.cc

Index: components/scheduler/renderer/task_cost_estimator.cc
diff --git a/components/scheduler/renderer/task_cost_estimator.cc b/components/scheduler/renderer/task_cost_estimator.cc
new file mode 100644
index 0000000000000000000000000000000000000000..cafbdd1b89fef1ed769cc84bdb0e69c335938396
--- /dev/null
+++ b/components/scheduler/renderer/task_cost_estimator.cc
@@ -0,0 +1,38 @@
+// 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_ = Now();
+}
+
+void TaskCostEstimator::DidProcessTask(const base::PendingTask& pending_task) {
+  if (--outstanding_task_count_ == 0) {
+    base::TimeDelta duration = Now() - task_start_time_;
+    rolling_time_delta_history_.InsertSample(duration);
+
+    // TODO(skyostil): Should we do this less often?
+    expected_task_duration_ =
+        rolling_time_delta_history_.Percentile(estimation_percentile_);
+  }
+}
+
+base::TimeTicks TaskCostEstimator::Now() {
+  return base::TimeTicks::Now();
+}
+
+}  // namespace scheduler