Remove AndroidRuntime::getJNIEnv() usage from libmediaplayer2

Test: pass MediaPlayer2Test#testPlayVideo
Bug: 63934228
Change-Id: I29da97cdc458bca18d95f4da349c93382e722727
diff --git a/media/libmediaplayer2/include/mediaplayer2/JavaVMHelper.h b/media/libmediaplayer2/include/mediaplayer2/JavaVMHelper.h
new file mode 100644
index 0000000..35091b7
--- /dev/null
+++ b/media/libmediaplayer2/include/mediaplayer2/JavaVMHelper.h
@@ -0,0 +1,40 @@
+/*
+ * Copyright 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.
+ */
+
+#ifndef JAVA_VM_HELPER_H_
+
+#define JAVA_VM_HELPER_H_
+
+#include "jni.h"
+
+#include <atomic>
+
+namespace android {
+
+struct JavaVMHelper {
+    static JNIEnv *getJNIEnv();
+    static void setJavaVM(JavaVM *vm);
+
+private:
+    // Once a valid JavaVM has been set, it should never be reset or changed.
+    // However, as it may be accessed from multiple threads, access needs to be
+    // synchronized.
+    static std::atomic<JavaVM *> sJavaVM;
+};
+
+}  // namespace android
+
+#endif  // JAVA_VM_HELPER_H_