[Mac] Shut down connections to WindowServer before engaging the sandbox.

The connection is only needed during sandbox warmup to initialize the default
color space. It was formerly needed by scrollbar NSAnimations, but that was
replaced via https://codereview.chromium.org/529103002/.

BUG=397642,306348
TEST=Manually tested on 10.6-10.10.
R=avi@chromium.org

Review URL: https://codereview.chromium.org/545603002

Cr-Commit-Position: refs/heads/master@{#293546}

content/renderer/renderer_main_platform_delegate_mac.mm

@@ -18,6 +18,11 @@
 #include "content/public/common/content_switches.h"
 #include "content/common/sandbox_init_mac.h"
 
+extern "C" {
+void CGSSetDenyWindowServerConnections(bool);
+void CGSShutdownServerConnections();
+};
+
 namespace content {
 
 namespace {
@@ -136,6 +141,12 @@ void RendererMainPlatformDelegate::PlatformUninitialize() {
 }
 
 bool RendererMainPlatformDelegate::EnableSandbox() {
+  // Disconnect from WindowServer before entering the sandbox, after all
+  // objects have been warmed up. Shutting down the connection requires
+  // connecting to WindowServer, so do this before engaging the sandbox.
+  CGSSetDenyWindowServerConnections(true);
+  CGSShutdownServerConnections();
+
   // Enable the sandbox.
   bool sandbox_initialized = InitializeSandbox();