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..a806ec20fe38663bc69892cb73da6106407852ac
--- /dev/null
+++ b/components/scheduler/renderer/task_cost_estimator.cc
@@ -0,0 +1,34 @@
+// 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)

[alex clarke (OOO till 29th), 2015/08/21 17:56:46]

Ack nested loops, we need a test sorry ;)

[Sami, 2015/08/21 18:14:42]

Agreed, bane of my existence, done.

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