color: Add enum value for the largest stock color.

Useful if we wish to keep a cache of patterns for the very common stock
colors...

src/cairo-color.c

@@ -67,13 +67,14 @@ _cairo_stock_color (cairo_stock_t stock)
 	return &cairo_color_black;
     case CAIRO_STOCK_TRANSPARENT:
 	return &cairo_color_transparent;
-    }
-
-    ASSERT_NOT_REACHED;
 
-    /* If the user can get here somehow, give a color that indicates a
-     * problem. */
-    return &cairo_color_magenta;
+    case CAIRO_STOCK_NUM_COLORS:
+    default:
+	ASSERT_NOT_REACHED;
+	/* If the user can get here somehow, give a color that indicates a
+	 * problem. */
+	return &cairo_color_magenta;
+    }
 }
 
 void

src/cairo-types-private.h

@@ -306,7 +306,8 @@ typedef struct _cairo_format_masks {
 typedef enum {
     CAIRO_STOCK_WHITE,
     CAIRO_STOCK_BLACK,
-    CAIRO_STOCK_TRANSPARENT
+    CAIRO_STOCK_TRANSPARENT,
+    CAIRO_STOCK_NUM_COLORS,
 } cairo_stock_t;
 
 typedef enum _cairo_image_transparency {