mojo: shell::Context should outlive the shell MessageLoop

mojo/shell/context.cc

Index: mojo/shell/context.cc
diff --git a/mojo/shell/context.cc b/mojo/shell/context.cc
index 159e3230d5236cac5a603e8d8ead01ecc935dbf0..88335156aa2de6f652cca823950493218a1caafe 100644
--- a/mojo/shell/context.cc
+++ b/mojo/shell/context.cc
@@ -83,9 +83,14 @@ class Context::NativeViewportServiceLoader : public ServiceLoader {
   DISALLOW_COPY_AND_ASSIGN(NativeViewportServiceLoader);
 };
 
-Context::Context()
-    : task_runners_(base::MessageLoop::current()->message_loop_proxy()) {
+Context::Context() {
+  DCHECK(!base::MessageLoop::current());
+}
+
+void Context::Init() {
   setup.Get();
+  task_runners_.reset(
+      new TaskRunners(base::MessageLoop::current()->message_loop_proxy()));
 
   for (size_t i = 0; i < arraysize(kLocalMojoURLs); ++i)
     mojo_url_resolver_.AddLocalFileMapping(GURL(kLocalMojoURLs[i]));
@@ -164,6 +169,7 @@ void Context::Shutdown() {
 }
 
 Context::~Context() {
+  DCHECK(!base::MessageLoop::current());
   Shutdown();
 }