exo: Implement lazy cursor changes.

components/exo/surface.h

Index: components/exo/surface.h
diff --git a/components/exo/surface.h b/components/exo/surface.h
index 63eefabcfb108718a6a3026da7076827857c880f..91ca1c688b71b0dfd0c85266c16c268857cb7d08 100644
--- a/components/exo/surface.h
+++ b/components/exo/surface.h
@@ -7,6 +7,7 @@
 
 #include <list>
 #include <memory>
+#include <set>
 #include <utility>
 
 #include "base/callback.h"
@@ -39,10 +40,15 @@ class Path;
 
 namespace exo {
 class Buffer;
+class Pointer;
 class SurfaceDelegate;
 class SurfaceObserver;
 class Surface;
 
+// The pointer class is currently the only cursor provider class but this can
+// change in the future when better hardware cursor support is added.
+using CursorProvider = Pointer;
+
 // This class owns the SurfaceFactory and keeps track of references to the
 // contents of Buffers. It's keeped alive by references from
 // release_callbacks_. It's destroyed when its owning Surface is destroyed and
@@ -167,6 +173,14 @@ class Surface : public aura::Window,
   // Returns the bounds of the surface area that is not know to be transparent.
   gfx::Rect GetNonTransparentBounds() const;
 
+  // Surface does not own cursor providers. It is the responsibility of the
+  // caller to remove the cursor provider before it is destroyed.
+  void RegisterCursorProvider(CursorProvider* provider);
+  void UnregisterCursorProvider(CursorProvider* provider);
+
+  // Returns true if surface has at least one cursor provider registered.
+  bool HasCursorProvider() const;
+
   // Set the surface delegate.
   void SetSurfaceDelegate(SurfaceDelegate* delegate);
 
@@ -305,6 +319,9 @@ class Surface : public aura::Window,
   // The compsitor being observer or null if not observing a compositor.
   ui::Compositor* compositor_;
 
+  // Cursor providers. Surface does not own the cursor providers.
+  std::set<CursorProvider*> cursor_providers_;
+
   // This can be set to have some functions delegated. E.g. ShellSurface class
   // can set this to handle Commit() and apply any double buffered state it
   // maintains.