wayland: don't prematurely release EGL buffers

commit 0165cb697466ba0843b993416e00d4f768c00d45 changed
mutter to release committed shm buffers as soon as they were
uploaded to the GPU.

It also inadvertently changed mutter to prematurely
release EGL buffers (which never get copied, but get used
directly).

This commit corrects that mistake.

https://bugzilla.gnome.org/show_bug.cgi?id=761312

src/wayland/meta-wayland-buffer.c

@@ -140,6 +140,9 @@ meta_wayland_buffer_ensure_texture (MetaWaylandBuffer *buffer)
 
   buffer->texture = texture;
 
+  if (shm_buffer)
+    buffer->copied_data = TRUE;
+
  out:
   return buffer->texture;
 }

src/wayland/meta-wayland-buffer.h

@@ -41,6 +41,7 @@ struct _MetaWaylandBuffer
   uint32_t ref_count;
 
   uint32_t accessible : 1;
+  uint32_t copied_data : 1;
 };
 
 MetaWaylandBuffer *     meta_wayland_buffer_from_resource       (struct wl_resource    *resource);

src/wayland/meta-wayland-surface.c

@@ -608,7 +608,7 @@ apply_pending_state (MetaWaylandSurface      *surface,
   if (!cairo_region_is_empty (pending->damage))
     surface_process_damage (surface, pending->damage);
 
-  if (pending->buffer)
+  if (pending->buffer && pending->buffer->copied_data)
     meta_wayland_buffer_release_control (pending->buffer);
 
   surface->offset_x += pending->dx;