First step to move common accessibility code out of content.

ui/accessibility/ax_export.h

Index: ui/accessibility/ax_export.h
diff --git a/ui/accessibility/ax_export.h b/ui/accessibility/ax_export.h
new file mode 100644
index 0000000000000000000000000000000000000000..59c66821d3995f4a927c258b5fe988cc994d5df3
--- /dev/null
+++ b/ui/accessibility/ax_export.h
@@ -0,0 +1,32 @@
+// Copyright (c) 2013 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_ACCESSIBILITY_AX_EXPORT_H_
+#define UI_ACCESSIBILITY_AX_EXPORT_H_
+
+// Defines AX_EXPORT so that functionality implemented by the
+// ui/accessibility module can be exported to consumers.
+
+#if defined(COMPONENT_BUILD)
+#if defined(WIN32)
+
+#if defined(ACCESSIBILITY_IMPLEMENTATION)
+#define AX_EXPORT __declspec(dllexport)
+#else
+#define AX_EXPORT __declspec(dllimport)
+#endif  // defined(ACCESSIBILITY_IMPLEMENTATION)
+
+#else  // defined(WIN32)
+#if defined(ACCESSIBILITY_IMPLEMENTATION)
+#define AX_EXPORT __attribute__((visibility("default")))
+#else
+#define AX_EXPORT
+#endif
+#endif
+
+#else  // defined(COMPONENT_BUILD)
+#define AX_EXPORT
+#endif
+
+#endif  // UI_ACCESSIBILITY_AX_EXPORT_H_