Better error message for anonymous class declarations

src/parser/statement.js

@@ -804,7 +804,7 @@ export default class StatementParser extends ExpressionParser {
       if (optionalId || !isStatement) {
         node.id = null;
       } else {
-        this.unexpected();
+        this.unexpected(null, "A class name is required");
       }
     }
   }

test/fixtures/es2015/uncategorised/263/options.json

@@ -1,3 +1,3 @@
 {
-  "throws": "Unexpected token (1:6)"
-}
+  "throws": "A class name is required (1:6)"
+}

test/fixtures/esprima/invalid-syntax/migrated_0261/options.json

@@ -1,3 +1,3 @@
 {
-  "throws": "Unexpected token (1:5)"
-}
+  "throws": "A class name is required (1:5)"
+}

test/fixtures/esprima/invalid-syntax/migrated_0262/options.json

@@ -1,3 +1,3 @@
 {
-  "throws": "Unexpected token (1:5)"
-}
+  "throws": "A class name is required (1:5)"
+}

test/fixtures/esprima/invalid-syntax/migrated_0263/options.json

@@ -1,3 +1,3 @@
 {
-  "throws": "Unexpected token (1:5)"
-}
+  "throws": "A class name is required (1:5)"
+}