Fix MojoChannelPerfTest.* tests failing in ipc_perftests on Mac.

ipc/ipc_test_base.cc

Index: ipc/ipc_test_base.cc
diff --git a/ipc/ipc_test_base.cc b/ipc/ipc_test_base.cc
index d09b3b69ad96dad409e96f41139d8c442a500a99..fd17b944bcc6bedeedb9448212f5e8f96d488197 100644
--- a/ipc/ipc_test_base.cc
+++ b/ipc/ipc_test_base.cc
@@ -13,7 +13,23 @@
 #include "build/build_config.h"
 #include "ipc/ipc_channel_mojo.h"
 
-IPCChannelMojoTestBase::IPCChannelMojoTestBase() = default;
+#if defined(OS_MACOSX) && !defined(OS_IOS)
+#include "base/mac/mach_port_broker.h"
+
+namespace {
+base::MachPortBroker* g_mach_broker = nullptr;
+}
+#endif
+
+IPCChannelMojoTestBase::IPCChannelMojoTestBase() {
+#if defined(OS_MACOSX) && !defined(OS_IOS)
+  if (!g_mach_broker) {
+    g_mach_broker = new base::MachPortBroker("mojo_test");
+    CHECK(g_mach_broker->Init());
+    mojo::edk::SetMachPortProvider(g_mach_broker);
+  }
+#endif
+}
 IPCChannelMojoTestBase::~IPCChannelMojoTestBase() = default;
 
 void IPCChannelMojoTestBase::Init(const std::string& test_client_name) {
@@ -24,12 +40,29 @@ void IPCChannelMojoTestBase::Init(const std::string& test_client_name) {
 void IPCChannelMojoTestBase::InitWithCustomMessageLoop(
     const std::string& test_client_name,
     std::unique_ptr<base::MessageLoop> message_loop) {
+#if defined(OS_MACOSX) && !defined(OS_IOS)
+  // This lock needs to be held while launching the child because the Mach port
+  // broker only allows task ports to be received from known child processes.
+  // However, it can only know the child process's pid after the child has
+  // launched. To prevent a race where the child process sends its task port
+  // before the pid has been registered, the lock needs to be held over both
+  // launch and child pid registration.
+  base::AutoLock lock(g_mach_broker->GetLock());
+#endif
   handle_ = helper_.StartChild(test_client_name);
+#if defined(OS_MACOSX) && !defined(OS_IOS)
+  g_mach_broker->AddPlaceholderForPid(helper_.test_child().Handle());
+#endif
   message_loop_ = std::move(message_loop);
 }
 
 bool IPCChannelMojoTestBase::WaitForClientShutdown() {
-  return helper_.WaitForChildTestShutdown();
+  int retval = helper_.WaitForChildTestShutdown();
+#if defined(OS_MACOSX) && !defined(OS_IOS)
+  base::AutoLock lock(g_mach_broker->GetLock());
+  g_mach_broker->InvalidatePid(helper_.test_child().Handle());
+#endif
+  return retval;
 }
 
 void IPCChannelMojoTestBase::TearDown() {