Fire accessibilityPrivate events on two-finger hold gesture.

ui/chromeos/touch_accessibility_enabler.h

 // Copyright 2016 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 UI_CHROMEOS_TOUCH_ACCESSIBILITY_ENABLER_H_
 #define UI_CHROMEOS_TOUCH_ACCESSIBILITY_ENABLER_H_
 
 #include "base/macros.h"
 #include "base/time/tick_clock.h"
 #include "base/timer/timer.h"
@@ skipping 12 matching lines @@
 class Event;
 class EventHandler;
 class TouchEvent;
 
 // A delegate to handle commands in response to detected accessibility gesture
 // events.
 class TouchAccessibilityEnablerDelegate {
  public:
   virtual ~TouchAccessibilityEnablerDelegate() {}
 
+  // Called when we first detect two fingers are held down.
+  virtual void OnTwoFingerTouchStart() {}
+
+  // Called when the user is no longer holding down two fingers (including
+  // releasing one, holding down three, or moving them).
+  virtual void OnTwoFingerTouchStop() {}
+

[oshima, 2017/04/10 18:32:08]

one suggestion. ash can use ui/chromeos, and chrome/browser/chromeos can
dependds on ash/ui/chromeos, so you could simply let the chrome/browser/chromeos
provides the implementation instead of invoking thorough ash,
AccessibilityDelegate creates the browser impl. (which can still be a single
instance)

[dmazzoni, 2017/04/10 18:54:50]

To clarify, you're saying AccessibiliiyManager (in
chrome/browser/chromeos/accessibility/) could implement
TouchAccessibilityEnablerDelegate and bypass ash entirely?

   // While the user holds down two fingers on a touch screen, which is the
   // gesture to enable spoken feedback (if held down long enough), play a sound
   // every "tick" (approximately every half-second) to warn the user something
   // is about to happen.
   virtual void PlaySpokenFeedbackToggleCountdown(int tick_count) {}
 
   // Toggles spoken feedback.
   virtual void ToggleSpokenFeedback() {}
 };
 
@@ skipping 67 matching lines @@
   // When touch_accessibility_enabler gets time relative to real time during
   // testing, this clock is set to the simulated clock and used.
   base::TickClock* tick_clock_;
 
   DISALLOW_COPY_AND_ASSIGN(TouchAccessibilityEnabler);
 };
 
 }  // namespace ui
 
 #endif  // UI_CHROMEOS_TOUCH_ACCESSIBILITY_ENABLER_H_