Add a new flag for demo

Bug: 287644619
Test: presubmit
Change-Id: Ic91d0f7e829a249dd6d1d8973d9c179b545d025b

samples/AconfigDemo/aconfig_demo_flags.aconfig

@@ -11,3 +11,9 @@ flag {
     namespace: "aconfig_demo_ns"
     description: "This flag controls static content"
 }
+
+flag {
+    name: "third_flag"
+    namespace: "configuration"
+    description: "This flag controls static content"
+}

samples/AconfigDemo/lib/com/example/android/aconfig/demo/StaticContent.java

@@ -17,6 +17,7 @@
 package com.example.android.aconfig.demo;
 
 import static com.example.android.aconfig.demo.flags.Flags.appendStaticContent;
+import static com.example.android.aconfig.demo.flags.Flags.thirdFlag;
 
 public class StaticContent {
 
@@ -32,6 +33,12 @@ public class StaticContent {
             sBuffer.append("The flag: appendStaticContent is OFF!!\n\n");
         }
 
+        if (thirdFlag()) {
+            sBuffer.append("The flag: thirdFlag is ON!!\n\n");
+        } else {
+            sBuffer.append("The flag: thirdFlag is OFF!!\n\n");
+        }
+
         return sBuffer.toString();
     }
 }