Add DVLOG with child process id in mojo shell.

services/shell/runner/host/child_process_host.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.
 
 #include "services/shell/runner/host/child_process_host.h"
 
 #include <stdint.h>
 
 #include <utility>
 
@@ skipping 181 matching lines @@
     MachBroker* mach_broker = MachBroker::GetInstance();
     base::AutoLock locker(mach_broker->GetLock());
 #endif
     child_process_ = base::LaunchProcess(*child_command_line, options);
 #if defined(OS_MACOSX)
     mach_broker->ExpectPid(child_process_.Handle());
 #endif
   }
 
   if (child_process_.IsValid()) {
+    DVLOG(0) << "Launched child process '" << target_.instance()

[Ken Rockot(use gerrit already), 2016/07/29 17:48:00]

I think this is a reasonable thing to do. You may want to log more than just the
instance though. Might as well log name, user_id, and instance?

[kylechar, 2016/07/29 17:59:34]

Yep, they could definitely come in handy. I added the extra fields.

+             << "' pid=" << child_process_.Pid();
     if (mojo_ipc_channel_.get()) {
       mojo_ipc_channel_->ChildProcessLaunched();
       mojo::edk::ChildProcessLaunched(
           child_process_.Handle(),
           mojo::edk::ScopedPlatformHandle(mojo::edk::PlatformHandle(
               mojo_ipc_channel_->PassServerHandle().release().handle)),
           child_token_);
     }
   }
   start_child_process_event_.Signal();
 }
 
 }  // namespace shell