added missing functions (#3877)

src/shapes/path_group.class.js

@@ -103,6 +103,52 @@
       ctx.restore();
     },
 
+    /**
+     * Decide if the object should cache or not.
+     * objectCaching is a global flag, wins over everything
+     * needsItsOwnCache should be used when the object drawing method requires
+     * a cache step. None of the fabric classes requires it.
+     * Generally you do not cache objects in groups because the group outside is cached.
+     * @return {Boolean}
+     */
+    shouldCache: function() {
+      var parentCache = this.objectCaching && (!this.group || this.needsItsOwnCache || !this.group.isCaching());
+      this.caching = parentCache;
+      if (parentCache) {
+        for (var i = 0, len = this.paths.length; i < len; i++) {
+          if (this.paths[i].willDrawShadow()) {
+            this.caching = false;
+            return false;
+          }
+        }
+      }
+      return parentCache;
+    },
+
+    /**
+     * Check if this object or a child object will cast a shadow
+     * @return {Boolean}
+     */
+    willDrawShadow: function() {
+      if (this.shadow) {
+        return true;
+      }
+      for (var i = 0, len = this.paths.length; i < len; i++) {
+        if (this.paths[i].willDrawShadow()) {
+          return true;
+        }
+      }
+      return false;
+    },
+
+    /**
+     * Check if this group or its parent group are caching, recursively up
+     * @return {Boolean}
+     */
+    isCaching: function() {
+      return this.caching || this.group && this.group.isCaching();
+    },
+
     /**
      * Check if cache is dirty
      */