Add initial implementation of cc::Surfaces backend for exo.

components/exo/shell_surface.cc

Index: components/exo/shell_surface.cc
diff --git a/components/exo/shell_surface.cc b/components/exo/shell_surface.cc
index 1f7c07b764808478e476400a124cb5aed02e6463..5529e5645e24ce133dece77c6f5f3102009fe9a3 100644
--- a/components/exo/shell_surface.cc
+++ b/components/exo/shell_surface.cc
@@ -945,7 +945,9 @@ void ShellSurface::UpdateWidgetBounds() {
   // should not result in a configure request.
   DCHECK(!ignore_window_bounds_changes_);
   ignore_window_bounds_changes_ = true;
-  widget_->SetBounds(new_widget_bounds);
+  if (current_bounds_ != new_widget_bounds)

[reveman, 2016/05/27 23:30:45]

nit: would be nice to land this as a separate patch unless it's actually
specific the use of surface layers

+    widget_->SetBounds(new_widget_bounds);
+  current_bounds_ = new_widget_bounds;
   ignore_window_bounds_changes_ = false;
 
   UpdateTransparentInsets();