Prioritize ARC instance only when it is needed

chrome/browser/chromeos/arc/boot_phase_monitor/arc_instance_throttle.h

Index: chrome/browser/chromeos/arc/boot_phase_monitor/arc_instance_throttle.h
diff --git a/chrome/browser/chromeos/arc/boot_phase_monitor/arc_instance_throttle.h b/chrome/browser/chromeos/arc/boot_phase_monitor/arc_instance_throttle.h
new file mode 100644
index 0000000000000000000000000000000000000000..476d75498f250b0b388fc78d44e46fe4d7beee64
--- /dev/null
+++ b/chrome/browser/chromeos/arc/boot_phase_monitor/arc_instance_throttle.h
@@ -0,0 +1,30 @@
+// Copyright 2017 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.
+
+#ifndef CHROME_BROWSER_CHROMEOS_ARC_BOOT_PHASE_MONITOR_ARC_INSTANCE_THROTTLE_H_
+#define CHROME_BROWSER_CHROMEOS_ARC_BOOT_PHASE_MONITOR_ARC_INSTANCE_THROTTLE_H_
+
+#include "ash/common/wm_activation_observer.h"
+#include "base/macros.h"
+
+namespace arc {
+
+// A class that watches window activations and throttle the ARC instance when

[Luis Héctor Chávez, 2017/01/11 00:07:28]

nit: s/throttle/throttles/

[Yusuke Sato, 2017/01/11 00:31:55]

Done.

+// needed.

[Luis Héctor Chávez, 2017/01/11 00:07:28]

maybe expand this comment a bit and mention that ARC is prioritized when one of
its windows is focused.

Also, when you unprioritize ARC, does it lower its priority below the baseline?
If so, maybe a better name for this would be ArcInstancePrioritizer.

[Yusuke Sato, 2017/01/11 00:31:55]

Done. Re class name, chatted offline and decided to keep the current class name.

+class ArcInstanceThrottle : public ash::WmActivationObserver {

[Luis Héctor Chávez, 2017/01/11 00:07:28]

Maybe "Throttler"? I've seen that Throttle has a different meaning in UI
context.

[Luis Héctor Chávez, 2017/01/11 00:10:19]

Hah, TIL that Throttle is the correct word and we've been using it wrong (in
favor of Throttler) more or less consistently throughout the codebase :P

+ public:
+  ArcInstanceThrottle();
+  ~ArcInstanceThrottle() override;
+
+  // ash::WmActivationObserver overrides:
+  void OnWindowActivated(ash::WmWindow* gained_active,
+                         ash::WmWindow* lost_active) override;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(ArcInstanceThrottle);
+};
+
+}  // namespace arc
+
+#endif  // CHROME_BROWSER_CHROMEOS_ARC_BOOT_PHASE_MONITOR_ARC_INSTANCE_THROTTLE_H_