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

ui/base/x/x11_util.cc

Index: ui/base/x/x11_util.cc
diff --git a/ui/base/x/x11_util.cc b/ui/base/x/x11_util.cc
index 873996fd451f7b7ae3cbe9798b332282b70de9d1..4beee61d2d6035c3eb2a550526838bd94786cd6b 100644
--- a/ui/base/x/x11_util.cc
+++ b/ui/base/x/x11_util.cc
@@ -113,12 +113,7 @@ 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) {
@@ -133,6 +128,15 @@ class XCursorCache {
     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_;
@@ -215,8 +219,15 @@ int GetDefaultScreen(Display* display) {
   return XDefaultScreen(display);
 }
 
+const int kCursorClearXCursorCache = -1;
 Cursor GetXCursor(int cursor_shape) {
   static XCursorCache cache;
+
+  if (cursor_shape == kCursorClearXCursorCache) {
+    cache.Clear();
+    return NULL;
+  }
+
   return cache.GetCursor(cursor_shape);
 }