exo: Add support for alpha_compositing interface to wayland bindings.

components/exo/surface.h

Index: components/exo/surface.h
diff --git a/components/exo/surface.h b/components/exo/surface.h
index 1bbb26431b6752a38735aa041992289e8427eb5b..417dba4c9fd8c28dcdb9d07f16fb9fb47b64bd1d 100644
--- a/components/exo/surface.h
+++ b/components/exo/surface.h
@@ -14,6 +14,7 @@
 #include "base/memory/weak_ptr.h"
 #include "base/observer_list.h"
 #include "third_party/skia/include/core/SkRegion.h"
+#include "third_party/skia/include/core/SkXfermode.h"
 #include "ui/aura/window.h"
 #include "ui/aura/window_observer.h"
 #include "ui/compositor/compositor_observer.h"
@@ -88,6 +89,12 @@ class Surface : public aura::Window,
   // appearing in screenshots or from being viewed on non-secure displays.
   void SetOnlyVisibleOnSecureOutput(bool only_visible_on_secure_output);
 
+  // This sets the blend mode that will be used when drawing the surface.
+  void SetBlendMode(SkXfermode::Mode blend_mode);

[Daniele Castagna, 2016/05/09 23:34:19]

nit: You can drop "This". Comments are usually imperative. I see the same "This
does" above though, so it can probably stay the same.

[reveman, 2016/05/10 14:05:19]

"This" all over place in this file so I'm going to keep it consistent and maybe
change it in a follow up.

+
+  // This sets the alpha value that will be applied to the whole surface.
+  void SetAlpha(float alpha);
+
   // Surface state (damage regions, attached buffers, etc.) is double-buffered.
   // A Commit() call atomically applies all pending state, replacing the
   // current state. Commit() is not guaranteed to be synchronous. See
@@ -198,6 +205,12 @@ class Surface : public aura::Window,
   // The secure output visibility state to take effect when Commit() is called.
   bool pending_only_visible_on_secure_output_;
 
+  // The blend mode state to take effect when Commit() is called.
+  SkXfermode::Mode pending_blend_mode_;

[Daniele Castagna, 2016/05/09 23:34:19]

Would it make sense to group all the pending state in a struct?

[reveman, 2016/05/10 14:05:19]

It might. I'll consider it for a follow up change.

+
+  // The alpha state to take effect when Commit() is called.
+  float pending_alpha_;
+
   // The buffer that is currently set as content of surface.
   base::WeakPtr<Buffer> current_buffer_;