Switch AccessibilityMode to be a bitmap

content/browser/accessibility/accessibility_mode_helper.cc

+// Copyright (c) 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.
+
+#include "content/browser/accessibility/accessibility_mode_helper.h"
+
+namespace content {
+
+unsigned int AddAccessibilityMode(unsigned int to,
+                                  AccessibilityMode mode_to_add) {
+  return to | mode_to_add;

[David Tseng, 2014/02/04 20:25:51]

Do we want to enforce which modes can be set at the same time?

[aboxhall, 2014/02/05 16:02:47]

I think editable text only overrides the other modes. Note that
AccessibilityModeComplete is just a shorthand for AccessibilityModeFlagRenderer
| AccessibilityModeFlagPlatform. Complete is the default, i.e. the 0 value for
AccessibilityModeFlagEditableTextOnly. 

+}
+
+unsigned int RemoveAccessibilityMode(unsigned int from,
+                                     AccessibilityMode mode_to_remove) {
+  if (!(mode_to_remove & AccessibilityModeFlagRenderer))
+    return from ^ (mode_to_remove & from);
+
+  unsigned int to_remove = mode_to_remove;
+
+  // AccessibilityModeFlagPlatform depends on AccessibilityModeFlagRenderer;
+  // don't turn off the latter if the former will remain on.
+  if (!(mode_to_remove & AccessibilityModeFlagPlatform) &&
+      (from & AccessibilityModeFlagPlatform)) {
+    to_remove ^= AccessibilityModeFlagRenderer;
+  }
+
+  return from ^ (to_remove & from);
+}
+
+}  // namespace content