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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_