[Aura] Support always-on-top top level window.

ui/base/x/x11_util.cc

 // Copyright (c) 2011 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.
 
 // This file defines utility functions for X11 (Linux only). This code has been
 // ported from XCB since we can't use XCB on Ubuntu while its 32-bit support
 // remains woefully incomplete.
 
 #include "ui/base/x/x11_util.h"
 
@@ skipping 95 matching lines @@
                             num_items,
                             &remaining_bytes,
                             property);
 }
 
 // A process wide singleton that manages the usage of X cursors.
 class XCursorCache {
  public:
    XCursorCache() {}
   ~XCursorCache() {
-    Display* display = base::MessagePumpForUI::GetDefaultXDisplay();
-    for (std::map<int, Cursor>::iterator it =
-        cache_.begin(); it != cache_.end(); ++it) {
-      XFreeCursor(display, it->second);
-    }
-    cache_.clear();
+    Clear();
   }
 
   Cursor GetCursor(int cursor_shape) {
     // Lookup cursor by attempting to insert a null value, which avoids
     // a second pass through the map after a cache miss.
     std::pair<std::map<int, Cursor>::iterator, bool> it = cache_.insert(
         std::make_pair(cursor_shape, 0));
     if (it.second) {
       Display* display = base::MessagePumpForUI::GetDefaultXDisplay();
       it.first->second = XCreateFontCursor(display, cursor_shape);
     }
     return it.first->second;
   }
 
+  void Clear() {
+    Display* display = base::MessagePumpForUI::GetDefaultXDisplay();
+    for (std::map<int, Cursor>::iterator it =
+        cache_.begin(); it != cache_.end(); ++it) {
+      XFreeCursor(display, it->second);
+    }
+    cache_.clear();
+  }
+
  private:
   // Maps X11 font cursor shapes to Cursor IDs.
   std::map<int, Cursor> cache_;
 
   DISALLOW_COPY_AND_ASSIGN(XCursorCache);
 };
 
 }  // namespace
 
 bool XDisplayExists() {
@@ skipping 64 matching lines @@
 
   return render_supported;
 }
 
 int GetDefaultScreen(Display* display) {
   return XDefaultScreen(display);
 }
 
 Cursor GetXCursor(int cursor_shape) {
   static XCursorCache cache;
+
+  if (cursor_shape == kCursorClearXCursorCache) {
+    cache.Clear();
+    return NULL;
+  }
+
   return cache.GetCursor(cursor_shape);
 }
 
 XID GetX11RootWindow() {
   return DefaultRootWindow(GetXDisplay());
 }
 
 bool GetCurrentDesktop(int* desktop) {
   return GetIntProperty(GetX11RootWindow(), "_NET_CURRENT_DESKTOP", desktop);
 }
@@ skipping 663 matching lines @@
       << "request_code " << static_cast<int>(error_event.request_code) << ", "
       << "minor_code " << static_cast<int>(error_event.minor_code)
       << " (" << request_str << ")";
 }
 
 // ----------------------------------------------------------------------------
 // End of x11_util_internal.h
 
 
 }  // namespace ui