sysprof: fix indent for non-expandable expanders

Instead of doing the indent depth trick that GtkTreeExpander does, this
changes the icon so that we keep the same indent size.

src/sysprof/icons/scalable/actions/empty-symbolic.svg

@@ -0,0 +1,35 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<svg
+   height="16px"
+   viewBox="0 0 16 16"
+   width="16px"
+   version="1.1"
+   id="svg5033"
+   sodipodi:docname="threads-symbolic.svg"
+   inkscape:version="1.2.2 (b0a8486541, 2022-12-01)"
+   xmlns:inkscape="http://www.inkscape.org/namespaces/inkscape"
+   xmlns:sodipodi="http://sodipodi.sourceforge.net/DTD/sodipodi-0.dtd"
+   xmlns="http://www.w3.org/2000/svg"
+   xmlns:svg="http://www.w3.org/2000/svg">
+  <defs
+     id="defs5037" />
+  <sodipodi:namedview
+     id="namedview5035"
+     pagecolor="#ffffff"
+     bordercolor="#666666"
+     borderopacity="1.0"
+     inkscape:showpageshadow="2"
+     inkscape:pageopacity="0.0"
+     inkscape:pagecheckerboard="0"
+     inkscape:deskcolor="#d1d1d1"
+     showgrid="false"
+     inkscape:zoom="51.007547"
+     inkscape:cx="7.1950137"
+     inkscape:cy="8.5771621"
+     inkscape:window-width="1551"
+     inkscape:window-height="1288"
+     inkscape:window-x="26"
+     inkscape:window-y="23"
+     inkscape:window-maximized="0"
+     inkscape:current-layer="svg5033" />
+</svg>

src/sysprof/style.css

@@ -43,6 +43,9 @@ callgraphview symbol {
   margin: -1px -3px;
   padding: 1px 6px;
 }
+callgraphview treeexpander expander:not(.expandable) {
+  -gtk-icon-source: -gtk-icontheme("empty-symbolic");
+}
 callgraphview row:not(:selected) treeexpander expander:checked+box symbol.process,
 callgraphview row:not(:selected) treeexpander expander:checked+box symbol.thread,
 callgraphview row:not(:selected) treeexpander expander:checked+box symbol.root {

src/sysprof/sysprof-tree-expander.c

@@ -126,6 +126,11 @@ sysprof_tree_expander_update_icon (SysprofTreeExpander *self)
           icon = self->icon;
           gtk_widget_unset_state_flags (self->expander, GTK_STATE_FLAG_CHECKED);
         }
+
+      if (gtk_tree_list_row_is_expandable (self->list_row))
+        gtk_widget_add_css_class (GTK_WIDGET (self->expander), "expandable");
+      else
+        gtk_widget_remove_css_class (GTK_WIDGET (self->expander), "expandable");
     }
 
   gtk_image_set_from_gicon (GTK_IMAGE (self->image), icon);

src/sysprof/sysprof.gresource.xml

@@ -4,6 +4,7 @@
     <file preprocess="xml-stripblanks">gtk/help-overlay.ui</file>
     <file preprocess="xml-stripblanks">gtk/menus.ui</file>
     <file preprocess="xml-stripblanks">icons/scalable/actions/address-layout-symbolic.svg</file>
+    <file preprocess="xml-stripblanks">icons/scalable/actions/empty-symbolic.svg</file>
     <file preprocess="xml-stripblanks">icons/scalable/actions/mark-chart-symbolic.svg</file>
     <file preprocess="xml-stripblanks">icons/scalable/actions/mark-table-symbolic.svg</file>
     <file preprocess="xml-stripblanks">icons/scalable/actions/mark-waterfall-symbolic.svg</file>