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

ui/gfx/screen_win.cc

Index: ui/gfx/screen_win.cc
===================================================================
--- ui/gfx/screen_win.cc	(revision 120215)
+++ ui/gfx/screen_win.cc	(working copy)
@@ -20,6 +20,9 @@
 namespace gfx {
 
 // static
+HDC Screen::compatible_dc_ = NULL;
+
+// static
 gfx::Point Screen::GetCursorScreenPoint() {
   POINT pt;
   GetCursorPos(&pt);
@@ -102,4 +105,19 @@
   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