Add a test for the version string presence.

Also verify that the version string appears in the default user agent.

Test: atest CtsNetHttpTestCases
Change-Id: I7bdfec745927d90e459382217c27514080e7143a
diff --git a/Cronet/tests/cts/src/android/net/http/cts/HttpEngineTest.java b/Cronet/tests/cts/src/android/net/http/cts/HttpEngineTest.java
index 0be3ea1..ccbf33a 100644
--- a/Cronet/tests/cts/src/android/net/http/cts/HttpEngineTest.java
+++ b/Cronet/tests/cts/src/android/net/http/cts/HttpEngineTest.java
@@ -211,6 +211,7 @@
     @Test
     public void testHttpEngine_GetDefaultUserAgent() throws Exception {
         assertThat(mEngineBuilder.getDefaultUserAgent(), containsString("AndroidHttpClient"));
+        assertThat(mEngineBuilder.getDefaultUserAgent()).contains(HttpEngine.getVersionString());
     }
 
     @Test
@@ -333,4 +334,9 @@
         UrlResponseInfo info = mCallback.mResponseInfo;
         assertOKStatusCode(info);
     }
-}
\ No newline at end of file
+
+    @Test
+    public void getVersionString_notEmpty() {
+        assertThat(HttpEngine.getVersionString()).isNotEmpty();
+    }
+}