mus: Show USER_PRIVATE window container during views tests

ui/views/mus/platform_test_helper_mus.cc

Index: ui/views/mus/platform_test_helper_mus.cc
diff --git a/ui/views/mus/platform_test_helper_mus.cc b/ui/views/mus/platform_test_helper_mus.cc
index df87e10ef87e61cee54912c423e6fe33905e064f..01ddeca45efaa844ccf3e5e1fc530f39092caa4e 100644
--- a/ui/views/mus/platform_test_helper_mus.cc
+++ b/ui/views/mus/platform_test_helper_mus.cc
@@ -6,6 +6,7 @@
 #include "base/files/file_path.h"
 #include "base/memory/ptr_util.h"
 #include "base/run_loop.h"
+#include "components/mus/common/switches.h"
 #include "services/shell/background/background_shell.h"
 #include "services/shell/background/tests/test_catalog_store.h"
 #include "services/shell/public/cpp/connector.h"
@@ -21,6 +22,12 @@ using shell::BackgroundShell;
 namespace views {
 namespace {
 
+void EnsureCommandLineSwitch(const std::string& name) {
+  base::CommandLine* cmd_line = base::CommandLine::ForCurrentProcess();
+  if (!cmd_line->HasSwitch(name))
+    cmd_line->AppendSwitch(name);
+}
+
 class DefaultShellClient : public shell::ShellClient {
  public:
   DefaultShellClient() {}
@@ -33,6 +40,11 @@ class DefaultShellClient : public shell::ShellClient {
 class PlatformTestHelperMus : public PlatformTestHelper {
  public:
   PlatformTestHelperMus() {
+    // Let other mojo apps know that we're running in tests. Do this with a
+    // command line flag to avoid making blocking calls to other processes for
+    // setup for tests (e.g. to unlock the screen in the window manager).
+    EnsureCommandLineSwitch(mus::switches::kUseTestConfig);
+
     background_shell_.reset(new BackgroundShell);
     background_shell_->Init(nullptr);
     shell_client_.reset(new DefaultShellClient);