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// Copyright (c) 2012 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 CONTENT_BROWSER_ACCESSIBILITY_BROWSER_ACCESSIBILITY_STATE_IMPL_H_
#define CONTENT_BROWSER_ACCESSIBILITY_BROWSER_ACCESSIBILITY_STATE_IMPL_H_
#pragma once
#include "base/basictypes.h"
#include "base/timer.h"
#include "content/public/browser/browser_accessibility_state.h"
template <typename T> struct DefaultSingletonTraits;
// The BrowserAccessibilityState class is used to determine if Chrome should be
// customized for users with assistive technology, such as screen readers. We
// modify the behavior of certain user interfaces to provide a better experience
// for screen reader users. The way we detect a screen reader program is
// different for each platform.
//
// Screen Reader Detection
// (1) On windows many screen reader detection mechinisms will give false
// positives like relying on the SPI_GETSCREENREADER system parameter. In Chrome
// we attempt to dynamically detect a MSAA client screen reader by calling
// NotifiyWinEvent in NativeWidgetWin with a custom ID and wait to see if the ID
// is requested by a subsequent call to WM_GETOBJECT.
// (2) On mac we detect dynamically if VoiceOver is running. We rely upon the
// undocumented accessibility attribute @"AXEnhancedUserInterface" which is set
// when VoiceOver is launched and unset when VoiceOver is closed. This is an
// improvement over reading defaults preference values (which has no callback
// mechanism).
class CONTENT_EXPORT BrowserAccessibilityStateImpl
: public BrowserAccessibilityState {
public:
virtual ~BrowserAccessibilityStateImpl();
static BrowserAccessibilityStateImpl* GetInstance();
virtual void OnAccessibilityEnabledManually() OVERRIDE;
virtual void OnScreenReaderDetected() OVERRIDE;
virtual bool IsAccessibleBrowser() OVERRIDE;
// Called a short while after startup to allow time for the accessibility
// state to be determined. Updates a histogram with the current state.
void UpdateHistogram();
protected:
BrowserAccessibilityStateImpl();
friend struct DefaultSingletonTraits<BrowserAccessibilityStateImpl>;
// Set to true when full accessibility features should be enabled.
bool accessibility_enabled_;
// Timer to update the histogram a short while after startup.
base::OneShotTimer<BrowserAccessibilityStateImpl> update_histogram_timer_;
DISALLOW_COPY_AND_ASSIGN(BrowserAccessibilityStateImpl);
};
#endif // CONTENT_BROWSER_ACCESSIBILITY_BROWSER_ACCESSIBILITY_STATE_IMPL_H_
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