Add support for constrained windows on os x, based on Avi's GTMWindowSheetController.

chrome/common/temp_scaffolding_stubs.cc

Index: chrome/common/temp_scaffolding_stubs.cc
diff --git a/chrome/common/temp_scaffolding_stubs.cc b/chrome/common/temp_scaffolding_stubs.cc
index b1d6f40c3bcd3d55e7f65ef6fb266d4b10deac9a..b72cb5ec7f8191778940bb286baba4e2b6f285b1 100644
--- a/chrome/common/temp_scaffolding_stubs.cc
+++ b/chrome/common/temp_scaffolding_stubs.cc
@@ -244,7 +244,7 @@ void MemoryDetails::StartFetch() {
   NOTIMPLEMENTED();
 }
 
-#if defined(OS_MACOSX) || (defined(OS_LINUX) && defined(TOOLKIT_VIEWS))
+#if defined(OS_LINUX) && defined(TOOLKIT_VIEWS)
 // This should prompt the user if she wants to allow more than one concurrent
 // download per tab. Until this is in place, always allow multiple downloads.
 class DownloadRequestDialogDelegateStub
@@ -252,7 +252,7 @@ class DownloadRequestDialogDelegateStub
  public:
   explicit DownloadRequestDialogDelegateStub(
     DownloadRequestManager::TabDownloadState* host)
-      : DownloadRequestDialogDelegate(host) { DoAccept(); }
+      : DownloadRequestDialogDelegate(host) { DoCancel(); }
 
   virtual void CloseWindow() {}
 };