Bug 1040939 - Fix startup error "Couldn't load XPCOM" Package sandboxbroker.dll r=ewong rs=bustagefix

Ports Firefox bugs:
Bug 933947 - Check for sandboxbroker.dll in use from the installer and uninstaller
Bug 985252 - Sandbox Gecko Media Plugins (including OpenH264) for Windows
-  Build sandbox code regardless of whether --enable-content-sandbox/MOZ_CONTENT_SANDBOX is provided.
-  Enable sandboxing of GMP plugins.
-  Enable `SandboxBroker` to set different security policies for different process types.