Revert "Revert "Make shell child processes slaves.""

This reverts commit 8a354f1948e5f28305e383813ee111cf201f6a2b.

I unreverted the revert of the stuff that it depended on.

TBR=yzshen@chromium.org

Review URL: https://codereview.chromium.org/1143993004
diff --git a/shell/shell_test_main.cc b/shell/shell_test_main.cc
index cad352b..92cdb62 100644
--- a/shell/shell_test_main.cc
+++ b/shell/shell_test_main.cc
@@ -15,7 +15,7 @@
   base::CommandLine::Init(argc, argv);
 
   CHECK(!base::CommandLine::ForCurrentProcess()->HasSwitch(
-      switches::kChildProcess));
+      switches::kChildConnectionId));
 
   base::TestSuite test_suite(argc, argv);
   return base::LaunchUnitTests(