Make content::DialogDelegate::GetDialogRootWindow() const.

BUG=none
TEST=none

Review URL: http://codereview.chromium.org/8725018

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@111859 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/content/browser/tab_contents/tab_contents.cc b/content/browser/tab_contents/tab_contents.cc
index 13e8ff4..aeb98c2 100644
--- a/content/browser/tab_contents/tab_contents.cc
+++ b/content/browser/tab_contents/tab_contents.cc
@@ -2021,7 +2021,7 @@
                                              user_input);
 }
 
-gfx::NativeWindow TabContents::GetDialogRootWindow() {
+gfx::NativeWindow TabContents::GetDialogRootWindow() const {
   return view_->GetTopLevelNativeWindow();
 }