add Stream::getTimestamp() to java api

android/filament-android/src/main/cpp/Stream.cpp

@@ -154,3 +154,9 @@ Java_com_google_android_filament_Stream_nReadPixels(JNIEnv *env, jclass,
 
     return 0;
 }
+
+extern "C" JNIEXPORT jlong JNICALL
+Java_com_google_android_filament_Stream_nGetTimestamp(JNIEnv*, jclass, jlong nativeStream) {
+    Stream *stream = (Stream *) nativeStream;
+    return stream->getTimestamp();
+}

android/filament-android/src/main/java/com/google/android/filament/Stream.java

@@ -128,6 +128,10 @@ public class Stream {
         }
     }
 
+    public long getTimestamp() {
+        return nGetTimestamp(getNativeObject());
+    }
+
     long getNativeObject() {
         if (mNativeObject == 0) {
             throw new IllegalStateException("Calling method on destroyed Stream");
@@ -153,6 +157,7 @@ public class Stream {
             Buffer storage, int remaining,
             int left, int top, int type, int alignment, int stride, int format,
             Object handler, Runnable callback);
+    private static native long nGetTimestamp(long nativeStream);
 
     private static native boolean nIsNative(long nativeStream);
 }