Implement fall-through errors.

test/kernel/regression/switch_execution_case_t02.dart

+/*
+ * Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
+ * for details. All rights reserved. Use of this source code is governed by a
+ * BSD-style license that can be found in the LICENSE file.
+ */
+
+// Slightly modified copy of
+// `co19/src/Language/Statements/Switch/execution_case_t02.dart`.
+
+/**
+ * @assertion Execution of a case clause case ek: sk of a switch statement
+ * switch (e) {label11 ..label1j1 case e1: s1 … labeln1 ..labelnjn case en: sn default: sn+1}
+ * proceeds as follows:
+ * The expression ek == id  is evaluated  to an object o which is then
+ * subjected to boolean conversion yielding a value v.
+ * If v is not true, the following case,  case ek+1: sk+1 is executed if it exists.
+ * If case ek+1: sk+1 does not exist, then the default clause is executed by executing sn+1.
+ * If v is true, let h be the smallest integer such that h >= k and sh is non-empty.
+ * If no such h exists, let h = n + 1. The sequence of statements sh is then executed.
+ * If execution reaches the point after sh  then a runtime error occurs, unless h = n + 1.
+ * @description Checks that falling through produces a runtime error, unless
+ * the current clause is an empty case clause or the default clause.
+ * @static-warning
+ * @author msyabro
+ * @reviewer rodionov
+ * @issue 7537
+ */
+
+test(value) {
+  var result;
+
+  switch(value) {
+    case 1:  result = 1;
+             break;
+    case 2:  result = 2; /// static warning - case fall-through, see "Switch"
+    case 3:  result = 3; /// static warning - case fall-through, see "Switch"
+    default: result = 4;
+  }
+  return result;
+}
+
+testEmptyCases(value) {
+  var result;
+
+  switch(value) {
+    case 1:
+    case 2: result = 1; /// static warning - case fall-through, see "Switch"
+    case 3:
+    case 4: result = 2;
+            break;
+    case 5:
+    case 6:
+    default:
+  }
+
+  return result;
+}
+
+main() {
+}