Gtk3 ui: Add libgtk3ui as a separate build component

chrome/browser/ui/libgtkui/libgtkui_export.h

Index: chrome/browser/ui/libgtkui/libgtkui_export.h
diff --git a/chrome/browser/ui/libgtkui/libgtkui_export.h b/chrome/browser/ui/libgtkui/libgtkui_export.h
new file mode 100644
index 0000000000000000000000000000000000000000..3d643493d4ad08c3bc49c3d19ec401ea1fb544d2
--- /dev/null
+++ b/chrome/browser/ui/libgtkui/libgtkui_export.h
@@ -0,0 +1,28 @@
+// 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 CHROME_BROWSER_UI_LIBGTKUI_LIBGTKUI_EXPORT_H_
+#define CHROME_BROWSER_UI_LIBGTKUI_LIBGTKUI_EXPORT_H_
+
+// Defines LIBGTKUI_EXPORT so that functionality implemented by our limited
+// gtk2 module can be exported to consumers.
+
+#if defined(COMPONENT_BUILD)
+#if defined(WIN32)
+
+#error "LIBGTKUI does not build on Windows."
+
+#else  // defined(WIN32)
+#if defined(LIBGTKUI_IMPLEMENTATION)
+#define LIBGTKUI_EXPORT __attribute__((visibility("default")))
+#else
+#define LIBGTKUI_EXPORT
+#endif
+#endif
+
+#else  // defined(COMPONENT_BUILD)
+#define LIBGTKUI_EXPORT
+#endif
+
+#endif  // CHROME_BROWSER_UI_LIBGTKUI_LIBGTKUI_EXPORT_H_