css: Make recomputing animated styles make more sense

When we look for what values need recomputing, we also determine what
value we are going to use to recompute. For values that contain
variables, that is the 'original' value, as returned by
gtk_css_style_get_original_value. For values that we recompute
because they may contain currentcolor, that is the specified value
as returned by gtk_css_animated_style_get_intrinsic_value.

The one issue here is that we currently don't preserve currentcolor
in the computed value, so recomputing the value does not do us
any good in the color case. That will be fixed separately.

gtk/gtkcssanimatedstyle.c

@@ -74,7 +74,6 @@ gtk_css_ ## NAME ## _values_recompute (GtkCssAnimatedStyle   *animated, \
                                        GtkCssAnimationChange  change) \
 { \
   GtkCssStyle *style = (GtkCssStyle *)animated; \
-  GtkCssValue **values = (GtkCssValue **)((guint8*)(animated->style->NAME) + sizeof (GtkCssValues)); \
   int i; \
 \
   for (i = 0; i < G_N_ELEMENTS (NAME ## _props); i++) \
@@ -82,28 +81,31 @@ gtk_css_ ## NAME ## _values_recompute (GtkCssAnimatedStyle   *animated, \
       guint id = NAME ## _props[i]; \
       GtkCssValue *original, *computed; \
       gboolean needs_recompute = FALSE; \
-\
-      if (values[i] == NULL) \
-        continue; \
 \
       original = gtk_css_style_get_original_value (style, id); \
-      if (original == NULL) \
-        continue; \
 \
       if ((change & GTK_CSS_ANIMATION_CHANGE_VARIABLES) && \
+           original && \
            gtk_css_value_contains_variables (original)) \
-        needs_recompute = TRUE; \
+        { \
+          needs_recompute = TRUE; \
+        } \
 \
       if ((change & GTK_CSS_ANIMATION_CHANGE_COLOR) && \
           property_has_color (id)) \
-        needs_recompute = TRUE; \
+        { \
+          needs_recompute = TRUE; \
+          if (original == NULL) \
+            original = gtk_css_animated_style_get_intrinsic_value (animated, id); \
+        } \
 \
       if (!needs_recompute) \
         continue; \
 \
-      computed = gtk_css_value_compute (original, \
-                                        id, \
-                                        context); \
+      if (original == NULL) \
+        continue; \
+\
+      computed = gtk_css_value_compute (original, id, context); \
       if (computed == NULL) \
         continue; \
 \