exo: Handle lost context situations properly.

components/exo/surface.h

 // Copyright 2015 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 COMPONENTS_EXO_SURFACE_H_
 #define COMPONENTS_EXO_SURFACE_H_
 
 #include <list>
 #include <utility>
 
@@ skipping 80 matching lines @@
 
   bool HasPendingDamageForTesting() const { return !pending_damage_.IsEmpty(); }
 
   // Overridden from views::View:
   gfx::Size GetPreferredSize() const override;
 
   // Overridden from ui::CompositorObserver:
   void OnCompositingDidCommit(ui::Compositor* compositor) override;
   void OnCompositingStarted(ui::Compositor* compositor,
                             base::TimeTicks start_time) override;
-  void OnCompositingEnded(ui::Compositor* compositor) override {}
-  void OnCompositingAborted(ui::Compositor* compositor) override {}
+  void OnCompositingEnded(ui::Compositor* compositor) override;
+  void OnCompositingAborted(ui::Compositor* compositor) override;
   void OnCompositingLockStateChanged(ui::Compositor* compositor) override {}
   void OnCompositingShuttingDown(ui::Compositor* compositor) override;
 
  private:
   bool needs_commit_surface_hierarchy() const {
     return needs_commit_surface_hierarchy_;
   }
 
-  bool has_contents() const { return has_contents_; }
+  // This returns true when the surface has some contents assigned to it.
+  bool has_contents() const { return !!current_buffer_; }
+
+  // This is true when Attach() has been called and new contents should take
+  // effect next time Commit() is called.
+  bool has_pending_contents_;
 
   // The buffer that will become the content of surface when Commit() is called.
   base::WeakPtr<Buffer> pending_buffer_;
 
   // The damage region to schedule paint for when Commit() is called.
   // TODO(reveman): Use SkRegion here after adding a version of
   // ui::Layer::SchedulePaint that takes a SkRegion.
   gfx::Rect pending_damage_;
 
   // These lists contains the callbacks to notify the client when it is a good
   // time to start producing a new frame. These callbacks move to
   // |frame_callbacks_| when Commit() is called. Later they are moved to
   // |active_frame_callbacks_| when the effect of the Commit() is reflected in
   // the compositor's active layer tree. The callbacks fire once we're notified
   // that the compositor started drawing that active layer tree.
   std::list<FrameCallback> pending_frame_callbacks_;
   std::list<FrameCallback> frame_callbacks_;
   std::list<FrameCallback> active_frame_callbacks_;
 
   // The opaque region to take effect when Commit() is called.
   SkRegion pending_opaque_region_;
 
   // The stack of sub-surfaces to take effect when Commit() is called.
   // Bottom-most sub-surface at the front of the list and top-most sub-surface
   // at the back.
   using SubSurfaceEntry = std::pair<Surface*, gfx::Point>;
   using SubSurfaceEntryList = std::list<SubSurfaceEntry>;
   SubSurfaceEntryList pending_sub_surfaces_;
 
+  // The buffer that is currently set as content of surface.
+  base::WeakPtr<Buffer> current_buffer_;
+
   // This is true if a call to Commit() as been made but
   // CommitSurfaceHierarchy() has not yet been called.
   bool needs_commit_surface_hierarchy_;
 
-  // This is true when surface has some contents assigned to it.
-  bool has_contents_;
+  // This is true when the contents of the surface should be updated next time
+  // the compositor successfully ends compositing.
+  bool update_contents_after_successful_compositing_;
 
   // The compsitor being observer or null if not observing a compositor.
   ui::Compositor* compositor_;
 
   // 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.
   SurfaceDelegate* delegate_;
 
   // Surface observer list. Surface does not own the observers.
   base::ObserverList<SurfaceObserver, true> observers_;
 
   DISALLOW_COPY_AND_ASSIGN(Surface);
 };
 
 }  // namespace exo
 
 #endif  // COMPONENTS_EXO_SURFACE_H_