Support auto-hide taskbar for panels on Windows.

views/widget/monitor_win.cc

Index: views/widget/monitor_win.cc
===================================================================
--- views/widget/monitor_win.cc	(revision 98834)
+++ views/widget/monitor_win.cc	(working copy)
@@ -4,7 +4,7 @@
 
 #include "views/widget/monitor_win.h"
 
-#include <windows.h>
+#include <shellapi.h>
 
 #include "base/logging.h"
 #include "ui/gfx/rect.h"
@@ -24,4 +24,14 @@
   return gfx::Rect();
 }
 
+HWND GetTopmostAutoHideTaskbarForEdge(UINT edge, HMONITOR monitor) {
+  APPBARDATA taskbar_data =  { sizeof APPBARDATA, NULL, 0, edge };
+  HWND taskbar = reinterpret_cast<HWND>(SHAppBarMessage(ABM_GETAUTOHIDEBAR,
+                                                        &taskbar_data));
+  return (::IsWindow(taskbar) && (monitor != NULL) &&
+         (MonitorFromWindow(taskbar, MONITOR_DEFAULTTONULL) == monitor) &&
+         (GetWindowLong(taskbar, GWL_EXSTYLE) & WS_EX_TOPMOST)) ?
+      taskbar : NULL;
+}
+
 }  // namespace views