exo: Add support for alpha_compositing interface to wayland bindings.

ui/compositor/layer.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_COMPOSITOR_LAYER_H_
 #define UI_COMPOSITOR_LAYER_H_
 
 #include <stddef.h>
 
 #include <memory>
@@ skipping 263 matching lines @@
   // Set new TextureMailbox for this layer. Note that |mailbox| may hold a
   // shared memory resource or an actual mailbox for a texture.
   void SetTextureMailbox(
       const cc::TextureMailbox& mailbox,
       std::unique_ptr<cc::SingleReleaseCallback> release_callback,
       gfx::Size texture_size_in_dip);
   void SetTextureSize(gfx::Size texture_size_in_dip);
   void SetTextureFlipped(bool flipped);
   bool TextureFlipped() const;
 
+  // The alpha value applied to the whole texture. The effective value of each
+  // pixel is computed as:
+  // pixel.a = pixel.a * alpha.
+  // Note: This is different from SetOpacity() as it only applies to the
+  // texture and child layers are unaffected.
+  // TODO(reveman): Remove once components/exo code is using SetShowSurface.
+  // crbug.com/610086
+  void SetTextureAlpha(float alpha);
+
   // Begins showing content from a surface with a particular id.
   void SetShowSurface(cc::SurfaceId surface_id,
                       const cc::SurfaceLayer::SatisfyCallback& satisfy_callback,
                       const cc::SurfaceLayer::RequireCallback& require_callback,
                       gfx::Size surface_size,
                       float scale,
                       gfx::Size frame_size_in_dip);
 
   bool has_external_content() {
     return texture_layer_.get() || surface_layer_.get();
@@ skipping 208 matching lines @@
   // The size of the frame or texture in DIP, set when SetShowDelegatedContent
   // or SetTextureMailbox was called.
   gfx::Size frame_size_in_dip_;
 
   DISALLOW_COPY_AND_ASSIGN(Layer);
 };
 
 }  // namespace ui
 
 #endif  // UI_COMPOSITOR_LAYER_H_