Improve multi-process debugging.

mojo/shell/child_process_host_unittest.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Note: This file also tests child_process.*.
 
 #include "mojo/shell/child_process_host.h"
 
 #include "base/logging.h"
 #include "base/macros.h"
 #include "base/message_loop/message_loop.h"
 #include "mojo/common/message_pump_mojo.h"
 #include "mojo/shell/context.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace mojo {
 namespace shell {
 namespace {
 
 // Subclass just so we can observe |DidStart()|.
 class TestChildProcessHost : public ChildProcessHost {
  public:
-  explicit TestChildProcessHost(Context* context) : ChildProcessHost(context) {}
+  explicit TestChildProcessHost(Context* context)
+      : ChildProcessHost(context, std::string()) {}
   ~TestChildProcessHost() override {}
 
   void DidStart(bool success) override {
     EXPECT_TRUE(success);
     ChildProcessHost::DidStart(success);
     base::MessageLoop::current()->QuitWhenIdle();
   }
 
  private:
   DISALLOW_COPY_AND_ASSIGN(TestChildProcessHost);
@@ skipping 19 matching lines @@
   int exit_code = child_process_host.Join();
   VLOG(2) << "Joined child: exit_code = " << exit_code;
   EXPECT_EQ(123, exit_code);
 
   context.Shutdown();
 }
 
 }  // namespace
 }  // namespace shell
 }  // namespace mojo