Fix crashes in ui::Compositor on Mac.

content/browser/renderer_host/render_widget_host_view_mac.h

Index: content/browser/renderer_host/render_widget_host_view_mac.h
diff --git a/content/browser/renderer_host/render_widget_host_view_mac.h b/content/browser/renderer_host/render_widget_host_view_mac.h
index 9e1aa1fe3746ef13dd2a5a34a6e8eabac98709d0..87bd1fac3d347cc83b31914c2180905316d44b4b 100644
--- a/content/browser/renderer_host/render_widget_host_view_mac.h
+++ b/content/browser/renderer_host/render_widget_host_view_mac.h
@@ -551,6 +551,10 @@ class CONTENT_EXPORT RenderWidgetHostViewMac
   // invoke it from the message loop.
   void ShutdownHost();
 
+  // Tear down all components of the browser compositor in an order that will
+  // ensure no dangling references.
+  void ShutdownBrowserCompositor();
+
   void EnsureBrowserCompositorView();
   void DestroyBrowserCompositorView();