Extend Clock interface with sleep method and add FakeClock.

The FakeClock allows to simulate timing behaviour including sleep time
for test cases.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=162345258

extensions/cronet/src/main/java/com/google/android/exoplayer2/ext/cronet/CronetDataSource.java

@@ -28,7 +28,6 @@ import com.google.android.exoplayer2.upstream.TransferListener;
 import com.google.android.exoplayer2.util.Assertions;
 import com.google.android.exoplayer2.util.Clock;
 import com.google.android.exoplayer2.util.Predicate;
-import com.google.android.exoplayer2.util.SystemClock;
 import java.io.IOException;
 import java.net.SocketTimeoutException;
 import java.net.UnknownHostException;
@@ -169,7 +168,7 @@ public class CronetDataSource extends UrlRequest.Callback implements HttpDataSou
       int connectTimeoutMs, int readTimeoutMs, boolean resetTimeoutOnRedirects,
       RequestProperties defaultRequestProperties) {
     this(cronetEngine, executor, contentTypePredicate, listener, connectTimeoutMs,
-        readTimeoutMs, resetTimeoutOnRedirects, new SystemClock(), defaultRequestProperties);
+        readTimeoutMs, resetTimeoutOnRedirects, Clock.DEFAULT, defaultRequestProperties);
   }
 
   /* package */ CronetDataSource(CronetEngine cronetEngine, Executor executor,

library/core/src/main/java/com/google/android/exoplayer2/util/Clock.java

@@ -16,16 +16,24 @@
 package com.google.android.exoplayer2.util;
 
 /**
- * An interface through which system clocks can be read. The {@link SystemClock} implementation
+ * An interface through which system clocks can be read. The {@link #DEFAULT} implementation
  * must be used for all non-test cases.
  */
 public interface Clock {
 
   /**
-   * Returns {@link android.os.SystemClock#elapsedRealtime}.
-   *
-   * @return Elapsed milliseconds since boot.
+   * Default {@link Clock} to use for all non-test cases.
+   */
+  Clock DEFAULT = new SystemClock();
+
+  /**
+   * @see android.os.SystemClock#elapsedRealtime().
    */
   long elapsedRealtime();
 
+  /**
+   * @see android.os.SystemClock#sleep(long).
+   */
+  void sleep(long sleepTimeMs);
+
 }

library/core/src/main/java/com/google/android/exoplayer2/util/SystemClock.java

@@ -18,11 +18,16 @@ package com.google.android.exoplayer2.util;
 /**
  * The standard implementation of {@link Clock}.
  */
-public final class SystemClock implements Clock {
+/* package */ final class SystemClock implements Clock {
 
   @Override
   public long elapsedRealtime() {
     return android.os.SystemClock.elapsedRealtime();
   }
 
+  @Override
+  public void sleep(long sleepTimeMs) {
+    android.os.SystemClock.sleep(sleepTimeMs);
+  }
+
 }

testutils/src/main/java/com/google/android/exoplayer2/testutil/FakeClock.java

@@ -0,0 +1,78 @@
+/*
+ * Copyright (C) 2017 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.
+ */
+package com.google.android.exoplayer2.testutil;
+
+import com.google.android.exoplayer2.util.Clock;
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * Fake {@link Clock} implementation independent of {@link android.os.SystemClock}.
+ */
+public final class FakeClock implements Clock {
+
+  private long currentTimeMs;
+  private final List<Long> wakeUpTimes;
+
+  /**
+   * Create {@link FakeClock} with an arbitrary initial timestamp.
+   *
+   * @param initialTimeMs Initial timestamp in milliseconds.
+   */
+  public FakeClock(long initialTimeMs) {
+    this.currentTimeMs = initialTimeMs;
+    this.wakeUpTimes = new ArrayList<>();
+  }
+
+  /**
+   * Advance timestamp of {@link FakeClock} by the specified duration.
+   *
+   * @param timeDiffMs The amount of time to add to the timestamp in milliseconds.
+   */
+  public synchronized void advanceTime(long timeDiffMs) {
+    currentTimeMs += timeDiffMs;
+    for (Long wakeUpTime : wakeUpTimes) {
+      if (wakeUpTime <= currentTimeMs) {
+        notifyAll();
+        break;
+      }
+    }
+  }
+
+  @Override
+  public long elapsedRealtime() {
+    return currentTimeMs;
+  }
+
+  @Override
+  public synchronized void sleep(long sleepTimeMs) {
+    if (sleepTimeMs <= 0) {
+      return;
+    }
+    Long wakeUpTimeMs = currentTimeMs + sleepTimeMs;
+    wakeUpTimes.add(wakeUpTimeMs);
+    while (currentTimeMs < wakeUpTimeMs) {
+      try {
+        wait();
+      } catch (InterruptedException e) {
+        // Ignore InterruptedException as SystemClock.sleep does too.
+      }
+    }
+    wakeUpTimes.remove(wakeUpTimeMs);
+  }
+
+}
+