exo: Add support for subcompositor interface.

components/exo/display.h

Index: components/exo/display.h
diff --git a/components/exo/display.h b/components/exo/display.h
index 472f4c96bc9d4ba24da3c95c9d72cd2166970b19..41099509a91c7ac0d73e024adc4ff14b49e8d211 100644
--- a/components/exo/display.h
+++ b/components/exo/display.h
@@ -12,6 +12,7 @@
 namespace exo {
 class SharedMemory;
 class ShellSurface;
+class SubSurface;
 class Surface;
 
 // The core display class. This class provides functions for creating surfaces
@@ -34,6 +35,10 @@ class Display {
   // Creates a shell surface for an existing surface.
   scoped_ptr<ShellSurface> CreateShellSurface(Surface* surface);
 
+  // Creates a sub-surface for an existing surface. The sub-surface will be
+  // a child of |parent|.
+  scoped_ptr<SubSurface> CreateSubSurface(Surface* surface, Surface* parent);
+
  private:
   DISALLOW_COPY_AND_ASSIGN(Display);
 };