Only shadow ARGB windows with a frame outside the frame

An ARGB window with a frame is likely something like a transparent
terminal. It looks awful (and breaks transparency) to draw a big
opaque black shadow under the window, so clip out the region under
the terminal from the shadow we draw.

Add meta_window_get_frame_bounds() to get a cairo region for the
outer bounds of the frame of a window, and modify the frame handling
code to notice changes to the frame shape and discard a cached
region. meta_frames_apply_shapes() is refactored so we can extract
meta_frames_get_frame_bounds() from it.

https://bugzilla.gnome.org/show_bug.cgi?id=635268

src/core/frame.c

@@ -328,7 +328,7 @@ meta_frame_calc_geometry (MetaFrame         *frame,
   *geomp = geom;
 }
 
-static void
+static gboolean
 update_shape (MetaFrame *frame)
 {
   if (frame->need_reapply_frame_shape)
@@ -339,10 +339,14 @@ update_shape (MetaFrame *frame)
                                  frame->rect.height,
                                  frame->window->has_shape);
       frame->need_reapply_frame_shape = FALSE;
+
+      return TRUE;
     }
+  else
+    return FALSE;
 }
 
-void
+gboolean
 meta_frame_sync_to_window (MetaFrame *frame,
                            int        resize_gravity,
                            gboolean   need_move,
@@ -350,8 +354,7 @@ meta_frame_sync_to_window (MetaFrame *frame,
 {
   if (!(need_move || need_resize))
     {
-      update_shape (frame);
-      return;
+      return update_shape (frame);
     }
 
   meta_topic (META_DEBUG_GEOMETRY,
@@ -401,6 +404,17 @@ meta_frame_sync_to_window (MetaFrame *frame,
         meta_ui_repaint_frame (frame->window->screen->ui,
                                frame->xwindow);
     }
+
+  return need_resize;
+}
+
+cairo_region_t *
+meta_frame_get_frame_bounds (MetaFrame *frame)
+{
+  return meta_ui_get_frame_bounds (frame->window->screen->ui,
+                                   frame->xwindow,
+                                   frame->rect.width,
+                                   frame->rect.height);
 }
 
 void