mus: Make --use-mus-in-renderer the default for --mash.

content/renderer/render_widget.cc

Index: content/renderer/render_widget.cc
diff --git a/content/renderer/render_widget.cc b/content/renderer/render_widget.cc
index d9edfea44b72f0dc3fcb4a0e2dc05dec9d3df7b1..32caa60d16d1a89d9474f652401f0334fa74dbe0 100644
--- a/content/renderer/render_widget.cc
+++ b/content/renderer/render_widget.cc
@@ -389,8 +389,8 @@ RenderWidget::RenderWidget(int32_t widget_routing_id,
     render_widget_scheduling_state_->SetHidden(is_hidden_);
   }
 #if defined(USE_AURA)
-  if (base::CommandLine::ForCurrentProcess()->HasSwitch(
-          switches::kUseMusInRenderer)) {
+  if (!base::CommandLine::ForCurrentProcess()->HasSwitch(
+          switches::kNoUseMusInRenderer)) {
     RendererWindowTreeClient::Create(routing_id_);
   }
 #endif
@@ -402,6 +402,15 @@ RenderWidget::~RenderWidget() {
   // If we are swapped out, we have released already.
   if (!is_swapped_out_ && RenderProcess::current())
     RenderProcess::current()->ReleaseProcess();
+#if defined(USE_AURA)
+  if (!base::CommandLine::ForCurrentProcess()->HasSwitch(
+          switches::kNoUseMusInRenderer)) {
+    // It is possible for a RenderWidget to be destroyed before it was embedded
+    // in a mus window. The RendererWindowTreeClient will leak in such cases. So
+    // explicitly delete it here.
+    RendererWindowTreeClient::Destroy(routing_id_);
+  }
+#endif
 }
 
 // static