Add rate limiter with default cold factor

extractor/src/test/java/org/schabi/newpipe/downloader/ratelimiting/limiter/RateLimiter.java

@@ -86,6 +86,39 @@ import java.util.concurrent.TimeUnit;
  * @since 13.0
  */
 public abstract class RateLimiter {
+    public static final double DEFAULT_COLD_FACTOR = 3.0;
+
+    /**
+     * Creates a {@code RateLimiter} with the specified stable throughput, given as "permits per
+     * second" (commonly referred to as <i>QPS</i>, queries per second), and a <i>warmup period</i>,
+     * during which the {@code RateLimiter} smoothly ramps up its rate, until it reaches its maximum
+     * rate at the end of the period (as long as there are enough requests to saturate it). Similarly,
+     * if the {@code RateLimiter} is left <i>unused</i> for a duration of {@code warmupPeriod}, it
+     * will gradually return to its "cold" state, i.e. it will go through the same warming up process
+     * as when it was first created.
+     *
+     * <p>The returned {@code RateLimiter} is intended for cases where the resource that actually
+     * fulfills the requests (e.g., a remote server) needs "warmup" time, rather than being
+     * immediately accessed at the stable (maximum) rate.
+     *
+     * <p>The returned {@code RateLimiter} starts in a "cold" state (i.e. the warmup period will
+     * follow), and if it is left unused for long enough, it will return to that state.
+     *
+     * @param permitsPerSecond the rate of the returned {@code RateLimiter}, measured in how many
+     *     permits become available per second
+     * @param warmupPeriod the duration of the period where the {@code RateLimiter} ramps up its rate,
+     *     before reaching its stable (maximum) rate
+     * @throws IllegalArgumentException if {@code permitsPerSecond} is negative or zero or {@code
+     *     warmupPeriod} is negative
+     * @since 28.0 (but only since 33.4.0 in the Android flavor)
+     */
+    public static RateLimiter create(
+            final double permitsPerSecond,
+            final Duration warmupPeriod
+    ) {
+        return create(permitsPerSecond, warmupPeriod, DEFAULT_COLD_FACTOR);
+    }
+
     /**
      * Creates a {@code RateLimiter} with the specified stable throughput, given as "permits per
      * second" (commonly referred to as <i>QPS</i>, queries per second), and a <i>warmup period</i>,