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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_
#include <vector>
#include "base/basictypes.h"
#include "base/compiler_specific.h"
#include "base/memory/singleton.h"
#include "content/common/view_message_enums.h"
#include "content/public/browser/browser_accessibility_state.h"
namespace content {
// 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 base::RefCountedThreadSafe<BrowserAccessibilityStateImpl>,
public BrowserAccessibilityState {
public:
BrowserAccessibilityStateImpl();
static BrowserAccessibilityStateImpl* GetInstance();
virtual void EnableAccessibility() OVERRIDE;
virtual void DisableAccessibility() OVERRIDE;
virtual void OnScreenReaderDetected() OVERRIDE;
virtual bool IsAccessibleBrowser() OVERRIDE;
virtual void AddHistogramCallback(base::Closure callback) OVERRIDE;
virtual void UpdateHistogramsForTesting() OVERRIDE;
AccessibilityMode accessibility_mode() const { return accessibility_mode_; };
void SetAccessibilityMode(AccessibilityMode mode);
private:
friend class base::RefCountedThreadSafe<BrowserAccessibilityStateImpl>;
friend struct DefaultSingletonTraits<BrowserAccessibilityStateImpl>;
// Called a short while after startup to allow time for the accessibility
// state to be determined. Updates histograms with the current state.
void UpdateHistograms();
// Leaky singleton, destructor generally won't be called.
virtual ~BrowserAccessibilityStateImpl();
void UpdatePlatformSpecificHistograms();
AccessibilityMode accessibility_mode_;
std::vector<base::Closure> histogram_callbacks_;
DISALLOW_COPY_AND_ASSIGN(BrowserAccessibilityStateImpl);
};
} // namespace content
#endif // CONTENT_BROWSER_ACCESSIBILITY_BROWSER_ACCESSIBILITY_STATE_IMPL_H_
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