wip: Second crack at implementing the touch exploration mode.

ui/aura/window_tree_host.h

Index: ui/aura/window_tree_host.h
diff --git a/ui/aura/window_tree_host.h b/ui/aura/window_tree_host.h
index 55d119e9953818760613dcae9a0b47a80de6b9c1..3c20c5da68fb59af138487e50dddf760e254e231 100644
--- a/ui/aura/window_tree_host.h
+++ b/ui/aura/window_tree_host.h
@@ -11,6 +11,7 @@
 #include "base/message_loop/message_loop.h"
 #include "ui/aura/aura_export.h"
 #include "ui/base/cursor/cursor.h"
+#include "ui/events/event_source.h"
 #include "ui/gfx/native_widget_types.h"
 
 namespace gfx {
@@ -65,6 +66,8 @@ class AURA_EXPORT WindowTreeHost {
 
   ui::Compositor* compositor() { return compositor_.get(); }
 
+  virtual ui::EventSource* GetEventSource() = 0;
+
   // Gets/Sets the root window's transform.
   virtual gfx::Transform GetRootTransform() const;
   virtual void SetRootTransform(const gfx::Transform& transform);