Mojo: Don't try to close the child process handle after WaitForExitCode().

mojo/shell/child_process_host.cc

Index: mojo/shell/child_process_host.cc
diff --git a/mojo/shell/child_process_host.cc b/mojo/shell/child_process_host.cc
index e743522e5ff16c757dc7d35948b6b60198eed8f5..5d797586e7c817e314e678299d2baa6345e49822 100644
--- a/mojo/shell/child_process_host.cc
+++ b/mojo/shell/child_process_host.cc
@@ -56,9 +56,9 @@ void ChildProcessHost::Start() {
 int ChildProcessHost::Join() {
   DCHECK_NE(child_process_handle_, base::kNullProcessHandle);
   int rv = -1;
+  // Note: |WaitForExitCode()| closes the process handle.
   LOG_IF(ERROR, !base::WaitForExitCode(child_process_handle_, &rv))
       << "Failed to wait for child process";
-  base::CloseProcessHandle(child_process_handle_);
   child_process_handle_ = base::kNullProcessHandle;
   return rv;
 }