Added suggested performance optimization

Author: bbtgp

src/parser/class.js

@@ -183,7 +183,7 @@ module.exports = {
          */
         function read_constant_declaration() {
           var result = this.node('classconstant'), name = null, value = null;
-          if (this.is('IDENTIFIER') || this.expect(this.tok.T_STRING)) {
+          if (this.token === this.tok.T_STRING || this.is('IDENTIFIER')) {
             name = this.text();
             this.next();
           }

src/parser/variable.js

@@ -127,23 +127,20 @@ module.exports = {
           result = node(result, offset);
           break;
         case this.tok.T_DOUBLE_COLON:
-          var node = this.node('staticlookup'), offset;
-          this.next();
-
-          if(this.is('IDENTIFIER') || this.token === this.tok.T_STRING
-              || this.token === this.tok.T_CLASS
-          ) {
-            offset = this.node('constref');
+          if((this.next().token === this.tok.T_STRING || this.is('IDENTIFIER'))) {
+            var node = this.node('staticlookup');
+            var offset = this.node('constref');
             var name = this.text();
+            
             this.next();
             offset = offset(name);
-
+            
             if(this.token === this.tok.T_OBJECT_OPERATOR || this.token === this.tok.T_DOUBLE_COLON) {
               this.error();
+            } else {
+              result = node(result, offset);
             }
           }
-
-          result = node(result, offset);
           break;
         case this.tok.T_OBJECT_OPERATOR:
           var node = this.node('propertylookup');