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 96619)
+++ 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 +24,17 @@
   return gfx::Rect();
 }
 
+// Returns true if edge |edge| (one of ABE_LEFT, TOP, RIGHT, or BOTTOM) of
+// monitor |monitor| has an auto-hiding taskbar that's always-on-top.
+bool EdgeHasTopmostAutoHideTaskbar(UINT edge, HMONITOR monitor) {
+  APPBARDATA taskbar_data = { 0 };
+  taskbar_data.cbSize = sizeof APPBARDATA;
+  taskbar_data.uEdge = 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);
+}
+
 }  // namespace views