Add a user id parameter to connections

mojo/shell/public/interfaces/shell.mojom

Index: mojo/shell/public/interfaces/shell.mojom
diff --git a/mojo/shell/public/interfaces/shell.mojom b/mojo/shell/public/interfaces/shell.mojom
index ed3cbd02a4096fc7faa4e157c47b2cfd72472b8d..11265a361a666fe32942cc77169da928a92a8b17 100644
--- a/mojo/shell/public/interfaces/shell.mojom
+++ b/mojo/shell/public/interfaces/shell.mojom
@@ -24,6 +24,8 @@ struct CapabilityFilter {
 // system and request connections to other applications.
 interface Shell {
   const uint32 kInvalidApplicationID = 0;
+  const uint32 kUserRoot = 0;
+  const uint32 kUserInherit = 1;
 
   // Establishes a connection with another application ("target application")
   // (located at |url|) through which the calling application and the
@@ -53,6 +55,7 @@ interface Shell {
   // application is permitted to connect to. See documentation for
   // CapabilityFilter above.
   Connect(string url,
+          uint32 user_id,

[sky, 2016/02/23 21:15:13]

Document what user_id means and how it's used.

           InterfaceProvider&? remote_interfaces,
           InterfaceProvider? local_interfaces,
           CapabilityFilter filter) => (uint32 application_id);