Use the default character set in CronetUrlRequestTest.

Since the TestUrlRequestCallback used by the test uses the default
encoding [1], the tests that use it should as well.

[1]
https://cs.chromium.org/chromium/src/components/cronet/android/test/javatests/src/org/chromium/net/TestUrlRequestCallback.java?l=242&rcl=6970d0e3493e5aec7c655313ef717140e68f790a

Change-Id: Ibdb32319a696fd9342a231c34eb235627712252c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1747251Reviewed-by: Paul Jensen <pauljensen@chromium.org>
Commit-Queue: Caleb Raitto <caraitto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#686435}

components/cronet/android/test/javatests/src/org/chromium/net/CronetUrlRequestTest.java

@@ -1575,7 +1575,7 @@ public class CronetUrlRequestTest {
         };
         UrlRequest.Builder builder = mTestFramework.mCronetEngine.newUrlRequestBuilder(
                 NativeTestServer.getEchoBodyURL(), callback, myExecutor);
-        UploadDataProvider dataProvider = UploadDataProviders.create("test".getBytes("UTF-8"));
+        UploadDataProvider dataProvider = UploadDataProviders.create("test".getBytes());
         builder.setUploadDataProvider(dataProvider, myExecutor);
         builder.addHeader("Content-Type", "useless/string");
         builder.allowDirectExecutor();