mash: Fix shutdown crashes by tearing down ServiceContext before message loop

chrome/app/mash/mash_runner.h

Index: chrome/app/mash/mash_runner.h
diff --git a/chrome/app/mash/mash_runner.h b/chrome/app/mash/mash_runner.h
index 75ffd0fbfffeb7f1999671341c0bb872b2b9bf08..db5c0956c31f14f24ac714a0154dc6d8df1c778f 100644
--- a/chrome/app/mash/mash_runner.h
+++ b/chrome/app/mash/mash_runner.h
@@ -10,10 +10,6 @@
 #include "base/macros.h"
 #include "services/service_manager/public/interfaces/service.mojom.h"
 
-namespace service_manager {
-class ServiceContext;
-}
-
 // Responsible for running mash, both child and main processes.
 class MashRunner {
  public:
@@ -39,9 +35,6 @@ class MashRunner {
 
   void StartChildApp(service_manager::mojom::ServiceRequest service_request);
 
-  // Context for service manager in the main process.
-  std::unique_ptr<service_manager::ServiceContext> context_;
-
   DISALLOW_COPY_AND_ASSIGN(MashRunner);
 };