css: Don't got to the selector tree for change

The tree is optimized for mimizing the decisions, and
that prevents us from taking advantage of the more exact
superset matching that we can do now. So, instead do what
we used to do for verifiation: use the tree for finding the
superset matches, then just walk the rulesets to collect the
changes.

gtk/gtkcssprovider.c

@@ -425,6 +425,33 @@ verify_tree_match_results (GtkCssProvider *provider,
 #endif
 }
 
+static GtkCssChange
+get_change (GtkCssProvider      *provider,
+            const GtkCssMatcher *matcher)
+{
+  GtkCssProviderPrivate *priv = gtk_css_provider_get_instance_private (provider);
+  GtkCssChange change = 0;
+  GPtrArray *tree_rules;
+  int i;
+
+  tree_rules = _gtk_css_selector_tree_match_all (priv->tree, matcher);
+  if (tree_rules)
+    {
+      for (i = tree_rules->len - 1; i >= 0; i--)
+        {
+	  GtkCssRuleset *ruleset;
+
+          ruleset = tree_rules->pdata[i];
+
+          change |= _gtk_css_selector_get_change (ruleset->selector);
+        }
+
+      g_ptr_array_free (tree_rules, TRUE);
+   }
+
+  return change;
+}
+
 static void
 verify_tree_get_change_results (GtkCssProvider *provider,
 				const GtkCssMatcher *matcher,
@@ -557,8 +584,7 @@ gtk_css_style_provider_lookup (GtkStyleProvider    *provider,
 
       _gtk_css_matcher_superset_init (&change_matcher, matcher, &matcher_class, GTK_CSS_CHANGE_CLASS | GTK_CSS_CHANGE_NAME);
 
-      *change = _gtk_css_selector_tree_get_change_all (priv->tree, &change_matcher);
-      verify_tree_get_change_results (css_provider, &change_matcher, *change);
+      *change = get_change (css_provider, &change_matcher);
     }
 }
 
@@ -745,7 +771,6 @@ parse_color_definition (GtkCssScanner *scanner)
   GtkCssValue *color;
   char *name;
 
-  if (!gtk_css_parser_try_at_keyword (scanner->parser, "define-color"))
     return FALSE;
 
   name = gtk_css_parser_consume_ident (scanner->parser);