add a read only flag for demo

Bug: 298754733
Test: atest AconfigDemoUnitTests
Change-Id: Ib01918b2469ea59091b47d49672800b5716beb88

samples/AconfigDemo/aconfig_demo_flags.aconfig

@@ -41,3 +41,11 @@ flag {
   description: "This flag controls static content"
   bug: "287644619"
 }
+
+flag {
+  name: "read_only_flag"
+  namespace: "core_experiments_team_internal"
+  description: "A read only flag for demo"
+  bug: "298754733"
+  is_fixed_read_only: true
+}

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

@@ -39,6 +39,12 @@ public class InjectedContent {
             sBuffer.append("The flag: appendInjectedContent is OFF!!\n\n");
         }
 
+        if (featureFlags.readOnlyFlag()) {
+            sBuffer.append("The flag: read only flag injected is ON!!\n\n");
+        } else {
+            sBuffer.append("The flag: read only flag injected is OFF!!\n\n");
+        }
+
         return sBuffer.toString();
     }
 }

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

@@ -18,6 +18,7 @@ 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;
+import static com.example.android.aconfig.demo.flags.Flags.readOnlyFlag;
 
 public class StaticContent {
 
@@ -39,6 +40,12 @@ public class StaticContent {
             sBuffer.append("The flag: thirdFlag is OFF!!\n\n");
         }
 
+        if (readOnlyFlag()) {
+            sBuffer.append("The flag: read only flag static is ON!!\n\n");
+        } else {
+            sBuffer.append("The flag: read only flag static is OFF!!\n\n");
+        }
+
         return sBuffer.toString();
     }
 }

samples/AconfigDemo/tests/unittests/StaticContentUnitTests.java

@@ -34,6 +34,7 @@ public final class StaticContentUnitTests {
     public void staticContent_enable_staticFlag_disable_thirdFlag() throws Exception {
         mSetFlagsRule.enableFlags(Flags.FLAG_APPEND_STATIC_CONTENT);
         mSetFlagsRule.disableFlags(Flags.FLAG_THIRD_FLAG);
+        mSetFlagsRule.disableFlags(Flags.FLAG_READ_ONLY_FLAG);
         StaticContent statiContent = new StaticContent();
         String ret = statiContent.getContent();
         StringBuilder expected = new StringBuilder();