Ensure tests check the return of SpawnChild() when they may wait without timeouts

content/common/sandbox_mac_unittest_helper.mm

Index: content/common/sandbox_mac_unittest_helper.mm
diff --git a/content/common/sandbox_mac_unittest_helper.mm b/content/common/sandbox_mac_unittest_helper.mm
index 564cc8b08556ed4476d7ea2cf3e859d112d242ee..3b0345d05d80171a6c5ad6d7b1f637f010610bd6 100644
--- a/content/common/sandbox_mac_unittest_helper.mm
+++ b/content/common/sandbox_mac_unittest_helper.mm
@@ -81,6 +81,10 @@ bool MacSandboxTest::RunTestInSandbox(Sandbox::SandboxProcessType sandbox_type,
 
   base::ProcessHandle child_process = SpawnChild("mac_sandbox_test_runner",
                                                  false);
+  if (child_process == base::kNullProcessHandle) {
+    LOG(WARNING) << "SpawnChild failed";
+    return false;
+  }
   int code = -1;
   if (!base::WaitForExitCode(child_process, &code)) {
     LOG(WARNING) << "base::WaitForExitCode failed";