mac: ensure ui::Compositor exists for visible RWHVs

content/public/test/test_renderer_host.cc

Index: content/public/test/test_renderer_host.cc
diff --git a/content/public/test/test_renderer_host.cc b/content/public/test/test_renderer_host.cc
index 35d4ca6e77d892f42b351e309739d0520510e535..342da6efd826cfcbb926330f8dd177ae4c4a8d04 100644
--- a/content/public/test/test_renderer_host.cc
+++ b/content/public/test/test_renderer_host.cc
@@ -37,6 +37,10 @@
 #include "ui/wm/core/default_activation_client.h"
 #endif
 
+#if defined(OS_MACOSX)
+#include "ui/accelerated_widget_mac/window_resize_helper_mac.h"
+#endif
+
 namespace content {
 
 // RenderFrameHostTester ------------------------------------------------------
@@ -200,7 +204,7 @@ void RenderViewHostTestHarness::SetUp() {
       new aura::test::AuraTestHelper(base::MessageLoopForUI::current()));
   aura_test_helper_->SetUp(context_factory);
   new wm::DefaultActivationClient(aura_test_helper_->root_window());
-#endif
+#endif  // USE_AURA
 
   sanity_checker_.reset(new ContentBrowserSanityChecker());
 
@@ -211,6 +215,13 @@ void RenderViewHostTestHarness::SetUp() {
 
   if (IsBrowserSideNavigationEnabled())
     BrowserSideNavigationSetUp();
+
+#if defined(OS_MACOSX)
+  if (!ui::WindowResizeHelperMac::Get()->task_runner()) {

[enne (OOO), 2016/05/26 00:07:06]

I'd love some feedback on what I should do here.  Here's the problem. 
content_unittests now creates a ui::Compositor where it didn't before.  In Mac
land, there's a dcheck that the WindowResizeHelperMac has a task runner
initialized on it.

This is a little bit weirdly global.  I think maybe the right thing to do here
is have a Shutdown() that clears it, so that I can always call Init/Shutdown
between tests when there aren't any compositors using this task runner?

Thoughts?

[ccameron, 2016/05/26 00:11:45]

Adding a Shutdown that tests use to clear this sounds reasonable.

+    ui::WindowResizeHelperMac::Get()->Init(
+      base::MessageLoop::current()->task_runner());
+  }
+#endif  // OS_MACOSX
 }
 
 void RenderViewHostTestHarness::TearDown() {