Create the Java Wrapper of RtpReceiverObserverInterface.

webrtc/sdk/android/src/jni/jni_helpers.h

Index: webrtc/sdk/android/src/jni/jni_helpers.h
diff --git a/webrtc/sdk/android/src/jni/jni_helpers.h b/webrtc/sdk/android/src/jni/jni_helpers.h
index 91f0a41a36dcd1eb597939b6bc57ef9a82c0a9d4..bed56838d5e4757f322a8263952a606b84691b57 100644
--- a/webrtc/sdk/android/src/jni/jni_helpers.h
+++ b/webrtc/sdk/android/src/jni/jni_helpers.h
@@ -62,11 +62,18 @@ jmethodID GetStaticMethodID(
 jfieldID GetFieldID(JNIEnv* jni, jclass c, const char* name,
                     const char* signature);
 
+jfieldID GetStaticFieldID(JNIEnv* jni,
+                          jclass c,
+                          const char* name,
+                          const char* signature);
+
 jclass GetObjectClass(JNIEnv* jni, jobject object);
 
 // Throws an exception if the object field is null.
 jobject GetObjectField(JNIEnv* jni, jobject object, jfieldID id);
 
+jobject GetStaticObjectField(JNIEnv* jni, jclass c, jfieldID id);
+
 jobject GetNullableObjectField(JNIEnv* jni, jobject object, jfieldID id);
 
 jstring GetStringField(JNIEnv* jni, jobject object, jfieldID id);