macOS V2 Sandbox: Allow PPAPI to contact window server.

Flash player DRM videos are currently broken because the V2 sandbox
blocks access to the window server. This allows the access.

Bug: 891823
Change-Id: I06116f1de78480fe80b01465a6b9b097066b7278
Reviewed-on: https://chromium-review.googlesource.com/c/1263282Reviewed-by: Mark Mentovai <mark@chromium.org>
Commit-Queue: Greg Kerr <kerrnel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#597169}

services/service_manager/sandbox/mac/ppapi_v2.sb

@@ -14,6 +14,10 @@
 ; Needed for Fonts.
 (allow-font-access)
 
+; Mach lookups.
+(allow mach-lookup
+  (global-name "com.apple.windowserver.active"))
+
 ; IOKit
 (allow iokit-open
   (iokit-registry-entry-class "IOSurfaceRootUserClient"))