Long press menu (shift+f6) to toggle spoken feedback.

ash/accelerators/key_hold_detector.h

+// Copyright 2014 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 ASH_ACCELERATOR_KEY_HOLD_DETECTOR_H_
+#define ASH_ACCELERATOR_KEY_HOLD_DETECTOR_H_
+
+#include "ash/ash_export.h"
+#include "base/memory/scoped_ptr.h"
+#include "ui/events/event_handler.h"
+
+namespace ui {
+class KeyEvent;
+}
+
+namespace ash {
+
+// This class is used to implement action when a user press and hold the key.
+// When a user just pressed and released a key, normal pressed event gets
+// generated upon release.
+class ASH_EXPORT KeyHoldDetector : public ui::EventHandler {
+ public:
+  class Delegate {
+   public:
+    virtual ~Delegate() {}
+
+    // If this return false, the event handler does not process
+    // the event at all.
+    virtual bool ShouldProcessEvent(const ui::KeyEvent* event) const = 0;
+
+    // This should return true if the event should start the state transition.
+    virtual bool IsStartEvent(const ui::KeyEvent* event) const = 0;
+
+    // Called when the key is held.
+    virtual void OnKeyHold(const ui::KeyEvent* event) = 0;
+
+    // Called when the key is release after hold.
+    virtual void OnKeyUnhold(const ui::KeyEvent* event) = 0;
+  };
+
+  explicit KeyHoldDetector(scoped_ptr<Delegate> delegate);
+  virtual ~KeyHoldDetector();
+
+  // ui::EventHandler overrides:
+  virtual void OnKeyEvent(ui::KeyEvent* key_event) OVERRIDE;
+
+ private:
+  // A state to keep track of one click and click and hold operation.
+  //
+  // One click:
+  // INITIAL --(first press)--> PRESSED --(release)--> INITIAL[SEND PRESS]
+  //
+  // Click and hold:
+  // INITIAL --(first press)--> PRESSED --(press)-->
+  //   HOLD[OnKeyHold] --(press)--> HOLD[OnKeyHold] --(release)-->
+  //   INITIAL[OnKeyUnhold]
+  enum State {
+    INITIAL,
+    PRESSED,
+    HOLD
+  };
+
+  State state_;
+  scoped_ptr<Delegate> delegate_;
+
+  DISALLOW_COPY_AND_ASSIGN(KeyHoldDetector);
+};
+
+}  // namespace ash
+
+#endif  // ASH_ACCELERATOR_KEY_HOLD_DETECTOR_H_