ART: Allow PackedSwitch instructions with zero targets

Optimizing and the interpreter wrongly assumed that a PackedSwitch
always has at least one target. This patch removes the corresponding
DCHECKs and adds a regression test case.

This is a resubmission of CL I32b7033ed38de6f1d1a6ee5d5bf12f3a47c9b37e

Bug: 21863783
Change-Id: I04e6e124bdd16591ba27c79490e6ce183c36b691
diff --git a/test/501-regression-packed-switch/src/Main.java b/test/501-regression-packed-switch/src/Main.java
new file mode 100644
index 0000000..b80bc62
--- /dev/null
+++ b/test/501-regression-packed-switch/src/Main.java
@@ -0,0 +1,33 @@
+/*
+ * Copyright (C) 2015 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import java.lang.reflect.Method;
+import java.lang.reflect.Type;
+
+public class Main {
+
+  // Workaround for b/18051191.
+  class InnerClass {}
+
+  public static void main(String args[]) throws Exception {
+    Class<?> c = Class.forName("Test");
+    Method m = c.getMethod("EmptyPackedSwitch", new Class[] { int.class });
+    Integer result = (Integer) m.invoke(null, new Integer(42));
+    if (result != 5) {
+      throw new Error("Expected 5, got " + result);
+    }
+  }
+}