Cache a screen compatible DC to avoid re-creating it excessively.

ui/gfx/screen_win.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.
 
 #include "ui/gfx/screen.h"
 
 #include <windows.h>
 
 namespace {
 
 MONITORINFO GetMonitorInfoForMonitor(HMONITOR monitor) {
   MONITORINFO monitor_info = { 0 };
   monitor_info.cbSize = sizeof(monitor_info);
   GetMonitorInfo(monitor, &monitor_info);
   return monitor_info;
 }
 
 }  // namespace
 
 namespace gfx {
 
 // static
+HDC Screen::compatible_dc_ = NULL;
+
+// static
 gfx::Point Screen::GetCursorScreenPoint() {
   POINT pt;
   GetCursorPos(&pt);
   return gfx::Point(pt);
 }
 
 // static
 gfx::Rect Screen::GetMonitorWorkAreaNearestWindow(gfx::NativeWindow window) {
   MONITORINFO monitor_info;
   monitor_info.cbSize = sizeof(monitor_info);
@@ skipping 62 matching lines @@
 gfx::Size Screen::GetPrimaryMonitorSize() {
   return gfx::Size(GetSystemMetrics(SM_CXSCREEN),
                    GetSystemMetrics(SM_CYSCREEN));
 }
 
 // static
 int Screen::GetNumMonitors() {
   return GetSystemMetrics(SM_CMONITORS);
 }
 
+// static
+HDC Screen::GetCompatibleDC() {
+  if (!compatible_dc_)
+    compatible_dc_ = CreateCompatibleDC(NULL);
+  return compatible_dc_;
+}
+
+// static
+void Screen::ReleaseCompatibleDC() {
+  if (compatible_dc_) {
+    DeleteDC(compatible_dc_);
+    compatible_dc_ = NULL;
+  }
+}
+
 }  // namespace gfx