Add test case for enable toString object view (#593)

Signed-off-by: Jinbo Wang <jinbwan@microsoft.com>

TestPlan.md

@@ -523,6 +523,13 @@ Exception in thread "main" java.lang.IllegalStateException
 
 ![image](https://user-images.githubusercontent.com/14052197/56104630-1e89d680-5f6b-11e9-87a5-8a17a2ed33b5.png)
 
+## Show toString object view
+1. Open `28.debugfeatures` project in VS Code.
+2. Open `Variables.java` file, and add a breakpoint at line 39.
+3. Click Debug CodeLens, check the Variable viewlet.
+4. Verify the highlight value in the screenshot below.
+![image](https://user-images.githubusercontent.com/14052197/58676978-c9741980-838c-11e9-9f0e-48658fa06bd7.png)
+
 ## Enable Java 12 preview for standalone Java files
 1. Install JDK-12.
 2. Open `28.debugfeatures` project in VS Code, and open `Java12Preview.java` file.

testprojects/28.debugfeatures/Variables.java

@@ -0,0 +1,75 @@
+import java.util.*;
+
+public class Variables {
+
+    public static void main(String[] args) {
+        int[] a = new int[100000];
+        Integer intObj = new Integer(20);
+        Float floatObj = new Float("1.354");
+        Character character = new Character('a');
+        Boolean bool = new Boolean(true);
+
+        Map<String, String> emptyMap = new HashMap<>();
+        Map<String, Integer> bookset = new LinkedHashMap<>();
+        bookset.put("Algorithm Introduction", 60);
+        bookset.put("Thinking in JAVA", 50);
+
+        Map<String, Map<String, Integer>> smallStore = new HashMap<>();
+        smallStore.put("Computer Science", bookset);
+
+        Map<String, Map<String, Integer>> bigStore = new HashMap<>();
+        for (int i = 0; i < 100000; i++) {
+            bigStore.put("key" + i, bookset);
+        }
+
+        List<String> smallList = Arrays.asList("Algorithm Introduction");
+        List<String> bigList = new ArrayList<>();
+        for (int i = 0; i < 100000; i++) {
+            bigList.add("key" + i);
+        }
+
+        School school = new School();
+        Person person = new Person();
+        Person person1 = null;
+        Employee employee = new Employee();
+        StringException stringException = new StringException();
+        NullString nullString =new NullString();
+        Date date = new Date();
+        String name = "Test";
+        System.out.println("Exit.");
+    }
+
+    public static class School {
+        String name = "test";
+
+    }
+
+    public static class Person {
+        String name = "jinbo";
+
+        @Override
+        public String toString() {
+            return "Person [name=" + name + "]";
+        }
+    }
+
+    public static class Employee extends Person {
+
+    }
+
+    public static class StringException {
+
+        @Override
+        public String toString() {
+            throw new RuntimeException("Unimplemented method exception");
+        }
+    }
+
+    public static class NullString {
+
+        @Override
+        public String toString() {
+            return null;
+        }
+    }
+}