Relanding "Multiprocess test client: Android child process launcher rework."

mojo/edk/test/multiprocess_test_helper.cc

Index: mojo/edk/test/multiprocess_test_helper.cc
diff --git a/mojo/edk/test/multiprocess_test_helper.cc b/mojo/edk/test/multiprocess_test_helper.cc
index 9aa9b0c6f7b9ec8c5f3face84c676a6f77993d2f..f5f9ce61a12c8609e0cd5b0b6e0360bb68cb927d 100644
--- a/mojo/edk/test/multiprocess_test_helper.cc
+++ b/mojo/edk/test/multiprocess_test_helper.cc
@@ -182,14 +182,8 @@ int MultiprocessTestHelper::WaitForChildShutdown() {
   CHECK(test_child_.IsValid());
 
   int rv = -1;
-#if defined(OS_ANDROID)
-  // On Android, we need to use a special function to wait for the child.
-  CHECK(AndroidWaitForChildExitWithTimeout(
-      test_child_, TestTimeouts::action_timeout(), &rv));
-#else
-  CHECK(
-      test_child_.WaitForExitWithTimeout(TestTimeouts::action_timeout(), &rv));
-#endif
+  WaitForMultiprocessTestChildExit(test_child_, TestTimeouts::action_timeout(),
+                                   &rv);
   test_child_.Close();
   return rv;
 }