Allow to specify initial bitrate estimate in DefaultBandwidthMeter.

This value is logically part of the bandwidth estimation and will eventually be
moved there from the adaptive track selection.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=187597038

library/core/src/main/java/com/google/android/exoplayer2/upstream/DefaultBandwidthMeter.java

@@ -16,6 +16,7 @@
 package com.google.android.exoplayer2.upstream;
 
 import android.os.Handler;
+import android.support.annotation.Nullable;
 import com.google.android.exoplayer2.util.Assertions;
 import com.google.android.exoplayer2.util.Clock;
 import com.google.android.exoplayer2.util.SlidingPercentile;
@@ -26,16 +27,94 @@ import com.google.android.exoplayer2.util.SlidingPercentile;
  */
 public final class DefaultBandwidthMeter implements BandwidthMeter, TransferListener<Object> {
 
-  /**
-   * The default maximum weight for the sliding window.
-   */
-  public static final int DEFAULT_MAX_WEIGHT = 2000;
+  /** Default initial bitrate estimate in bits per second. */
+  public static final long DEFAULT_INITIAL_BITRATE_ESTIMATE = BandwidthMeter.NO_ESTIMATE;
+
+  /** Default maximum weight for the sliding window. */
+  public static final int DEFAULT_SLIDING_WINDOW_MAX_WEIGHT = 2000;
+
+  /** Builder for a bandwidth meter. */
+  public static final class Builder {
+
+    private @Nullable Handler eventHandler;
+    private @Nullable EventListener eventListener;
+    private long initialBitrateEstimate;
+    private int slidingWindowMaxWeight;
+    private Clock clock;
+
+    /** Creates a builder with default parameters and without listener. */
+    public Builder() {
+      initialBitrateEstimate = DEFAULT_INITIAL_BITRATE_ESTIMATE;
+      slidingWindowMaxWeight = DEFAULT_SLIDING_WINDOW_MAX_WEIGHT;
+      clock = Clock.DEFAULT;
+    }
+
+    /**
+     * Sets an event listener for new bandwidth estimates.
+     *
+     * @param eventHandler A handler for events.
+     * @param eventListener A listener of events.
+     * @return This builder.
+     * @throws IllegalArgumentException If the event handler or listener are null.
+     */
+    public Builder setEventListener(Handler eventHandler, EventListener eventListener) {
+      Assertions.checkArgument(eventHandler != null && eventListener != null);
+      this.eventHandler = eventHandler;
+      this.eventListener = eventListener;
+      return this;
+    }
+
+    /**
+     * Sets the maximum weight for the sliding window.
+     *
+     * @param slidingWindowMaxWeight The maximum weight for the sliding window.
+     * @return This builder.
+     */
+    public Builder setSlidingWindowMaxWeight(int slidingWindowMaxWeight) {
+      this.slidingWindowMaxWeight = slidingWindowMaxWeight;
+      return this;
+    }
+
+    /**
+     * Sets the initial bitrate estimate in bits per second that should be assumed when a bandwidth
+     * estimate is unavailable.
+     *
+     * @param initialBitrateEstimate The initial bitrate estimate in bits per second.
+     * @return This builder.
+     */
+    public Builder setInitialBitrateEstimate(long initialBitrateEstimate) {
+      this.initialBitrateEstimate = initialBitrateEstimate;
+      return this;
+    }
+
+    /**
+     * Sets the clock used to estimate bandwidth from data transfers. Should only be set for testing
+     * purposes.
+     *
+     * @param clock The clock used to estimate bandwidth from data transfers.
+     * @return This builder.
+     */
+    public Builder setClock(Clock clock) {
+      this.clock = clock;
+      return this;
+    }
+
+    /**
+     * Builds the bandwidth meter.
+     *
+     * @return A bandwidth meter with the configured properties.
+     */
+    public DefaultBandwidthMeter build() {
+      return new DefaultBandwidthMeter(
+          eventHandler, eventListener, initialBitrateEstimate, slidingWindowMaxWeight, clock);
+    }
+  }
 
   private static final int ELAPSED_MILLIS_FOR_ESTIMATE = 2000;
   private static final int BYTES_TRANSFERRED_FOR_ESTIMATE = 512 * 1024;
 
-  private final Handler eventHandler;
-  private final EventListener eventListener;
+  private final @Nullable Handler eventHandler;
+  private final @Nullable EventListener eventListener;
   private final SlidingPercentile slidingPercentile;
   private final Clock clock;
 
@@ -47,25 +126,44 @@ public final class DefaultBandwidthMeter implements BandwidthMeter, TransferList
   private long totalBytesTransferred;
   private long bitrateEstimate;
 
+  /** Creates a bandwidth meter with default parameters. */
   public DefaultBandwidthMeter() {
-    this(null, null);
+    this(
+        /* eventHandler= */ null,
+        /* eventListener= */ null,
+        DEFAULT_INITIAL_BITRATE_ESTIMATE,
+        DEFAULT_SLIDING_WINDOW_MAX_WEIGHT,
+        Clock.DEFAULT);
   }
 
+  /** @deprecated Use {@link Builder} instead. */
+  @Deprecated
   public DefaultBandwidthMeter(Handler eventHandler, EventListener eventListener) {
-    this(eventHandler, eventListener, DEFAULT_MAX_WEIGHT);
+    this(
+        eventHandler,
+        eventListener,
+        DEFAULT_INITIAL_BITRATE_ESTIMATE,
+        DEFAULT_SLIDING_WINDOW_MAX_WEIGHT,
+        Clock.DEFAULT);
   }
 
+  /** @deprecated Use {@link Builder} instead. */
+  @Deprecated
   public DefaultBandwidthMeter(Handler eventHandler, EventListener eventListener, int maxWeight) {
-    this(eventHandler, eventListener, maxWeight, Clock.DEFAULT);
+    this(eventHandler, eventListener, DEFAULT_INITIAL_BITRATE_ESTIMATE, maxWeight, Clock.DEFAULT);
   }
 
-  public DefaultBandwidthMeter(Handler eventHandler, EventListener eventListener, int maxWeight,
+  private DefaultBandwidthMeter(
+      @Nullable Handler eventHandler,
+      @Nullable EventListener eventListener,
+      long initialBitrateEstimate,
+      int maxWeight,
       Clock clock) {
     this.eventHandler = eventHandler;
     this.eventListener = eventListener;
     this.slidingPercentile = new SlidingPercentile(maxWeight);
     this.clock = clock;
-    bitrateEstimate = NO_ESTIMATE;
+    bitrateEstimate = initialBitrateEstimate;
   }
 
   @Override
@@ -98,9 +196,7 @@ public final class DefaultBandwidthMeter implements BandwidthMeter, TransferList
       slidingPercentile.addSample((int) Math.sqrt(sampleBytesTransferred), bitsPerSecond);
       if (totalElapsedTimeMs >= ELAPSED_MILLIS_FOR_ESTIMATE
           || totalBytesTransferred >= BYTES_TRANSFERRED_FOR_ESTIMATE) {
-        float bitrateEstimateFloat = slidingPercentile.getPercentile(0.5f);
-        bitrateEstimate = Float.isNaN(bitrateEstimateFloat) ? NO_ESTIMATE
-            : (long) bitrateEstimateFloat;
+        bitrateEstimate = (long) slidingPercentile.getPercentile(0.5f);
       }
     }
     notifyBandwidthSample(sampleElapsedTimeMs, sampleBytesTransferred, bitrateEstimate);
@@ -120,5 +216,4 @@ public final class DefaultBandwidthMeter implements BandwidthMeter, TransferList
       });
     }
   }
-
 }