Add test that DefaultDataSource is able to build an RtmpDataSource

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=222387374

extensions/rtmp/build.gradle

@@ -33,6 +33,8 @@ dependencies {
     implementation project(modulePrefix + 'library-core')
     implementation 'net.butterflytv.utils:rtmp-client:3.0.1'
     implementation 'com.android.support:support-annotations:' + supportLibraryVersion
+    testImplementation 'junit:junit:' + junitVersion
+    testImplementation 'org.robolectric:robolectric:' + robolectricVersion
 }
 
 ext {

extensions/rtmp/src/test/AndroidManifest.xml

@@ -0,0 +1,17 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- Copyright (C) 2018 The Android Open Source Project
+
+     Licensed under the Apache License, Version 2.0 (the "License");
+     you may not use this file except in compliance with the License.
+     You may obtain a copy of the License at
+
+          http://www.apache.org/licenses/LICENSE-2.0
+
+     Unless required by applicable law or agreed to in writing, software
+     distributed under the License is distributed on an "AS IS" BASIS,
+     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+     See the License for the specific language governing permissions and
+     limitations under the License.
+-->
+
+<manifest package="com.google.android.exoplayer2.ext.rtmp"/>

extensions/rtmp/src/test/java/com/google/android/exoplayer2/ext/rtmp/DefaultDataSourceTest.java

@@ -0,0 +1,45 @@
+/*
+ * Copyright (C) 2018 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.google.android.exoplayer2.ext.rtmp;
+
+import android.net.Uri;
+import com.google.android.exoplayer2.upstream.DataSpec;
+import com.google.android.exoplayer2.upstream.DefaultDataSource;
+import java.io.IOException;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.robolectric.RobolectricTestRunner;
+import org.robolectric.RuntimeEnvironment;
+
+/** Unit test for {@link DefaultDataSource} with RTMP URIs. */
+@RunWith(RobolectricTestRunner.class)
+public final class DefaultDataSourceTest {
+
+  @Test
+  public void openRtmpDataSpec_instantiatesRtmpDataSourceViaReflection() throws IOException {
+    DefaultDataSource dataSource =
+        new DefaultDataSource(
+            RuntimeEnvironment.application, "userAgent", /* allowCrossProtocolRedirects= */ false);
+    DataSpec dataSpec = new DataSpec(Uri.parse("rtmp://test.com/stream"));
+    try {
+      dataSource.open(dataSpec);
+    } catch (UnsatisfiedLinkError e) {
+      // RtmpDataSource was successfully instantiated (test run using Gradle).
+    } catch (UnsupportedOperationException e) {
+      // RtmpDataSource was successfully instantiated (test run using Blaze).
+    }
+  }
+}