Merge backout of changeset 6b686281f9ac (Bug 445765) for causing a 3% Txul (Twinopen) regression on Linux.

layout/base/nsLayoutUtils.cpp

@@ -88,7 +88,6 @@
 #include "imgIRequest.h"
 #include "imgIContainer.h"
 #include "nsIImageLoadingContent.h"
-#include "nsCOMPtr.h"
 
 #ifdef MOZ_SVG
 #include "nsSVGUtils.h"
@@ -3152,13 +3151,13 @@ nsLayoutUtils::GetDeviceContextForScreenInfo(nsIDocShell* aDocShell)
 
     win->EnsureSizeUpToDate();
 
-    nsRefPtr<nsPresContext> presContext;
-    docShell->GetPresContext(getter_AddRefs(presContext));
-    if (presContext) {
-      nsIDeviceContext* context = presContext->DeviceContext();
-      if (context) {
-        return context;
-      }
+    nsCOMPtr<nsIBaseWindow> baseWindow = do_QueryInterface(docShell);
+    NS_ENSURE_TRUE(baseWindow, nsnull);
+
+    nsCOMPtr<nsIWidget> mainWidget;
+    baseWindow->GetMainWidget(getter_AddRefs(mainWidget));
+    if (mainWidget) {
+      return mainWidget->GetDeviceContext();
     }
 
     nsCOMPtr<nsIDocShellTreeItem> curItem = do_QueryInterface(docShell);